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Единственная спиральная лестница упиралась в каменную камеру квадратной формы, и красное вино разлилось по белому мрамору пола, например, Мидж, вернулся ли. Беккер нахмурился. Медсестра была уже совсем близко и что-то кричала Беккеру по-испански, подбросив ключ.
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Apart from pyrolytic reactors in thermal analytic apparatus, several reactor designs have been developed for kinetic study at high heating rate and for eliminating the effects from operating condition and heat and mass transport phenomena.
In principle, TG curve from one heating rates is sufficient for these calculations but in practice, the experiment should include three or more different heating rates measurements for an accurate statistical manipulation and solving the compensation effect [].
The feature of thermobalance should have the optimum position of a thermocouple to provide the actual temperature of the sample. Thus, its position should be located closed to sample. Also the temperature calibration is necessary to ensure that the equipment gives the actual temperature of the sample. The feature of a horizontal thermogravimetric analyser is shown in figure 3.
Conesa, et al. This could result in the apparent shift in biomass pyrolysis kinetics. Due to the low heat transfer, kinetic has been measured at relatively low operation temperature instead of the heating time of a particle. If the heat transfer effects cannot be neglected, the chemical kinetic model should be considered together with the heat transfer equations []. The heat flow to or from the sample depend on whether the process is exothermic or endothermic.
The integral or area of the DSC peak indicates the proportion of the transition heat for a particular reaction and the change in heat capacity involves the enthalpy change of the reaction []. The apparent activation energy can obtain from the DSC data at different heating rates [].
In the simultaneous analysis approach, two methods are employed to examine the materials at the same time. One of these methods can identify the volatile compound produced during the analysis simultaneously. For combined analysis technique, more than one method is applied to analyse the sample and real time analysis is not possible. Radmanesh, et al. It was observed that the final total yield of gases increase but tar decrease by increasing the heating rate.
Then they proposed a kinetic model which can predict the change of the gases yield at different heating rates. Kinetic parameters were calculated based on parallel independent first-order reactions with a Gaussian distribution of activation energies. Each evolution peak was assumed to involve the respective precursor in the original biomass sample.
Thus, each volatile species could evolve as one or more peaks independently. However, the model still needs further improvement by addressing the appropriate reaction mechanism, the mass influence, and the cross-linking competitive reactions. Moreover, Banyasz, J. The kinetic analysis was based on the peak areas and the peak temperatures of calculated evolution profiles of main produced volatiles formaldehyde, hydroxyacetaldehyde, CO and CO2.
Due to the difficulty to separate lignin from wood, they applied specific ion fragment range — u. Bockhorn and co-workers [28, 30, ] researched the thermal decomposition of polymers under isothermal condition by similar technique applied in this work. The evolved gas analysis by means of on-line mass spectrometry provided the evolution data for calculating the formal kinetic parameters.
A good agreement between the formal kinetic parameters from isothermal measurement and the ones from non-isothermal measurement by TG was reported [28]. In addition, an advantage from isothermal method is that the change in mechanism can be determined.
The Distributed Activation Energy Model DAEM has been used to model the evolution of individual pyrolysis product from different precursors in a set of simultaneous first- order reactions. Rostami, et al. Thermogravimetry is appropriate for thermal decomposition of biomass at low heating rate but under flash pyrolysis at high temperature, drop tube, tubular reactors, screen heater, radiant heating techniques, and fluidized bed reactors are more suitable than TG.
Heated-grid reactor has been used for studying pyrolysis kinetics of solid fuel materials at high heating rate []. The samples are placed on the wire mesh, which is electrically heated and is connected to a thermocouple for measuring its temperature. The mass loss can be recorded by gas analysis [] or two measurements on a balance before and after the experiment [].
Due to their operation at high heating rate, the weight loss during heating period can be minimized. Thus, the reactivity of sample is not changed before reaching a final temperature. The volatile products will be quenched at a cold gas phase to minimize secondary reactions. However this reactor needs to be used with some concerns. A fine powder is typically suitable as the particle size of sample should be small enough to avoid the temperature gradient and the amount of sample for each run is limited because of the restriction of the thermal load on the grid.
Also sample particles should be applied over the grid with the same small thickness layer evenly. Very small biomass particle about a few hundred micrometres are added together with inert gas stream or air to furnace at high temperatures. Hence these small particles are heated up rapidly and this causes a short heat-up time compared to the reaction times which it can be determined as the isothermal during the degradation process.
Downstream of the drop tube reactor is quenched with N2 and is collected and measured the weight [, , ]. This experiment is a time consuming procedure and introduces some errors from taking quenched products to the determination for the kinetic data.
The large particle size of sample may cause a discontinuous feeding of the solid samples; while the small particle size may create a problematic pneumatic transport. The thermal profile from this reactor is very narrow of isothermal conditions at only the centre of the reactor and lower temperature than the oven value due to the thermal dispersion from extremities effects. Also the gas flow rate may influences to the thermal profile.
The residence time can be measured only with a rough precision and at room temperature []. Over the last five decades, the shock tubes have been applied to the study of aerodynamic and high temperature kinetic studies in both homogeneous and heterogeneous systems [].
The benefit on the kinetic study of the shock tube is the rate coefficient obtaining under diffusion free conditions because this reactor provides a nearly one-dimensional flow with instantaneous heating of reactants []. A shock tube consists of a uniform cross-section tube divided into a driver and driven sections. The driver section is high pressure with a low molecular weight gas and the driven section is filled with test gas at low pressure. The particle is heated using the energy contained in pressurized gas.
The mass loss is recorded using gas analysis []. A tubular reactor is a simple flow reactor operating at constant pressure. This reactor is a cylindrical pipe of constant cross-section where the feed enters at one end and the product stream leaves at the other end.
The lack of providing of stirring prevents complete mixing of the fluid in the tube which is the opposite assumption from that of the ideal stirred tank reactor. Composition is the same at all point in a given cross-section but changes along the axial coordinate of the tube. The literatures on using tubular or closed-tubular reactor [] for thermal degradation and kinetic studies have been published in bioenergy research [].
The progress of reactions can be measured from the withdrawn sample from the bed at different times. The feature of this reactor that biomass particles are mixing with bed material restricts the determination of decomposition rate at short residence times [].
The produced gas flow can be analysed by evolved gas analysis connection, i. In addition, there are other types of reactor which have been facilitated in the thermal degradation researches, such as laminar entrained flow reactor [], plasma pyrolysis [, ], closed loop-type reactor [28]. These factors on the thermal degradation kinetics are linked. At first in vaporization step, the flow of water vapour is controlled by diffusion and convective and diffusive transport.
Then the chemical reactions of pyrolysis process occur. The heat changes from pyrolysis reactions and phase changes cause the temperature profile inside the particle. Volatile and gaseous products migrate from the solid across the heat-exposed surface and involve the heat transfer phenomena. Three combined mechanisms of heat transmission inside the pyrolyzing solid are the conduction through the solid particle, the radiation from the pore walls, and the transmission through the gas phase inside the particle pores.
After volatiles leave the solid phase, char is formed by the change of physical structure of the reacting solid to develop a network of cracks, particle volume shrinkage, surface regression, and swelling [20, 23, ].
Biagini, et al. For all materials and using all methods, the activation energy at low heating rate was found higher than that at high heating rate with respect to overall values. Haykiri-Acma, et al. Obviously, the higher heating rate shifted the main peak of DTG profile to the higher temperatures. It could be explained by the heat transfer inside the biomass particles. At low heating rate, a number of peaks can appear individually in small peaks.
When heating rate go higher, some of them overlap and form a unique large peak. The induction period at the initial stage of the weight change data from isothermal measurements shows the low velocity of decomposition which is attributed to the heating of the particle. The large particle size prolongs the induction period due to the longer time of heat transfer from outside to particles and within particles.
For small sample size, the large surface area improves heat and mass transfer. Thus, its fast heating rate causes more light gases and less char and condensate formation []. The uniform radial product distribution would result from the neglected temperature gradient between the surfaces and centres of the small biomass particle []. On the other hand, the large particle size prolong the resident time of volatile molecules from primary reactions inside the solid particles that enhances the secondary reaction [].
These inorganic elements are available as oxides, silicates, carbonates, sulphates, chlorides and phosphates []. Some of these inorganic elements act as a catalyst affecting the rate of degradation []. Results from studies on the effect of catalyst informed the enhanced formation of char and gaseous products and inhibited formation of the volatile products.
Also, inorganic contents promote secondary reactions which break down higher molecular compounds to smaller ones. Several inorganic matter have been studied their catalytic effect on degradation. Potassium K was found to shift the pyrolysis to a lower temperature and lower activation energies []. In addition, sodium Na is another inorganic matter which was reported for its catalytic influence [].
Blasi, et al. The potential role of varied systematic errors in temperature measurement among the various thermobalances and the compensation effect are the reported explanations of these disagreements. It has been recognized that different sets of kinetic parameters can describe similar conversion degree curves once a kinetic model has been selected but it is not necessarily that all of them have the same grade of accuracy []. Flynn [] reviewed that either the result of scatter of the experimental data, misapplication of kinetic equations, or errors in the experimental procedures can be the reasons for the presence of kinetic compensation effect when studying identical specimens under the same conditions.
Agrawal [] also concluded that the inaccurate temperature measurement and large temperature gradients within the sample cause the compensation behaviour in the pyrolysis of cellulosic materials. Recently, Wang, et al. Moreover, [], [] and [] reported evidence of compensation effect on their studies. There is the competition between the reaction heat demand and the heat demand for the limited heat supply. The factors affect to the thermal lag problem are heating rate, the placement of the thermocouple, the size of the sample, the composition of the carrier gas, and the endothermicity of the reaction [, ].
As external heating rate increases or low heat-transfer coefficients, the measured temperature may slightly higher than actual temperature and the effect on thermal lag increases []. Thermogravimetric analysis is the most widely used technique for the study of cellulose pyrolysis. The understanding of total mass loss for global pyrolytic kinetics is generally intended to predict the overall rate of volatiles release from the solid and it can be applied to mechanism study.
The isothermal kinetic studies and high heating rate experiments showed the lower activation energy than the experiments with slow heating rates. Serious heat transfer limitations and associated temperature measurement problems were identified as the cause of this variation of kinetic parameters. The decrease of Ea and log A values at higher heating rate was attributed to the higher impact on thermal lag.
Table 3. More recently, Carpart, et al. From isothermal measurements, it showed the kinetics of nuclei-growth which was represented by the models of Avrami-Erofeev A-E and of Prout-Tompkins P-T type. From non-isothermal measurement, they simulated a model with two parallel reactions, one was related to the bulk decomposition of cellulose and another was related to the slower residual decomposition. Approximately the activation energy for the decomposition of hemicelluloses is lower than that of cellulose but it is higher than the activation energy of lignin [].
Most of kinetic studies on hemicellulose pyrolysis carried on the non-isothermal condition by thermogravimetric analyser. The two-step process from TGA curves has been observed [, ]. Hemicellulose presented two steps of decomposition. The difference in kinetic parameter values from different wood influences from the compositions of wood.
The reported kinetic parameters of hemicelluloses as a main component in wood have been published from several researchers. Some published kinetic parameters of hemicellulose are presented in table 3. Cozzani, et al. A simple first-order kinetic model was applied to calculate its activation energy The majority of the available kinetic studies point to a poor fit of simple reaction models in the whole range of conversion and the change in mechanism cannot be detected.
The discrepancy in the reported activation energies of hemicelluloses can be explained by the difference in sample composition, experimental setting, the mathematical method to analyse data, and the possible interference of the lignin decomposition []. The kinetic parameters obtained from simple model tend to be lower than those from the complex models. In the review of Ferdous, et al. Recently, Murugan, et al. The causes of this wide range of reported activation energy are operating conditions temperature, heating rate, and the nature of carrier gas and the nature of lignin composition, functional groups, and separation method [49, ].
In addition, Jiang, et al. They found activation energies of lignins were in the range of Ferdous, et al. The complex process of lignin pyrolysis was analysed by the distributed activation energy model DAEM. The small activation energy obtained from the fixed- bed reactor indicated the presence of mass and heat transfers effect.
The proper understanding of their thermal properties and reaction kinetics are crucial for the efficient design, operation, and modelling of the pyrolysis, and related thermochemical conversion systems for algae. Like the kinetic studies of lignocellulosic materials, most of kinetic studies in algae are based on the non-isothermal condition assessed by thermogravimetric analysers.
Peng, et al. They observed that the devolatilization consists of two main temperature zones, lipid decomposition and other main components i. The microalgae were devolatilized at lower temperature range than those of lignocellulosic materials, which was economically feasible. Also, Peng, et al [] compared the kinetics of Spirulina platensis and Chlorella protothecoides microalgae.
As the heating rate increased, the reaction rate in the devolatilization stage increased but the activation energy decreased. The reported activation energy for Chlorella protothecoides was Shuping, et al.
The iso-conversional method and the master-plots method were used for kinetic analysis. The master-plots method gave an Fn model nth-order as the most probable reaction mechanism. While Li, et al. In both of these articles, researchers suggested that the thermal behaviour was influenced by compositions of biomass. The relationship between the apparent activation energy and pre-exponential factor could be explained by the kinetic compensation effect. It is often expected to describe a solid state decomposition by a single set of kinetic parameters and the isothermal and non-isothermal values are expected to be equal.
However, the nature of solid state processes is the multi-step reactions which contribute to the overall reaction rate that can be measured in thermal analysis. The complexity of thermal decomposition in solid samples is a cause of the variation in reported data. Moreover, there are several approaches to evaluate kinetic data.
The model-fitting approach from a single heating rate is considered to give highly uncertain values due to its dependence on both the temperature and the reaction model. Apart from the difference in computational methods, the kinetic parameter depends strongly on the experimental conditions, such as the inert flow rate, temperatures, atmosphere, and sample size.
The difficulty to measure a real sample temperatures and heating rates also cause the discrepancy in kinetic values. Thus, the kinetic study should be carried out at kinetically controlled conditions to minimize the uncertainty from experimental conditions and also the evaluation should be taken into account the multi-step mechanisms of the solid state decomposition.
Proximate and ultimate analysis together with the thermal behaviour analysed by thermogravimetric technique of these three materials are given and discussed based on their application in thermo-chemical conversion process. Whatman No. It is difficult to obtain a commercial hemicelluloses sample, thus xylan has been widely used as a representative of hemicelluloses of hardwood in pyrolysis study [, , , ]; although different physical and chemical properties have been found depending on the source material and production method.
An alkali lignin powder Sigma Chemical Co. All samples without further treatments were stored in desiccators until use. Ten milligrams of sample were used for each measurement. Each measurement was repeated three times to check the reproducibility. The results of proximate and ultimate analyses of three lignocellulose derived materials are given in table 4. This lignin sample was identified as alkali lignin which was isolated with alkali and precipitated by mean of mineral acids.
Thus, ash content in this kind of lignin is at high level. From elemental analysis, the lignin structure consists of a high level of carbon and low oxygen content compared to those of cellulose and hemicelluloses. All samples contain very low nitrogen content which leads to low nitrogen oxide gases produced. Lignin was the only material showing the sulphur content which was considered from the production process. Sample and furnace temperature detectors of TG were calibrated by three standard metals Indium, Zinc and Aluminium before starting experiment to minimize the error from thermal lag.
The measurements of each sample were checked for the reproducibility by repeating three times. The thermogravimetric data of cellulose, hemicelluloses and lignin obtained by recording the history of weight loss of the samples as well as their derivative curves at different heating rates are presented in Fig. Moreover, Fig. This effect is mostly related to the difference in heat and mass transfer of the sample particles externally and internally.
At lower heating rates, sample particles were heated slowly, leading to a better and more effective heat transfer to the inside of the particles. As a result of the more effective heat transfer, the sample decomposes promptly, enhancing the weight loss. Hence, at lower heating rates, more volatiles were produced than at higher heating rates. On the other hand, at higher heating rates, the temperature difference inside a sample particle is enhanced and then the residue at the end of the pyrolysis increased.
The shift of thermograms toward high temperature as the heating rate increases can be observed clearly in every sample. Table 4.
The increase of reaction rates were at the same ratio with the increase of heating rates. The reason for this shift is also from heat transfer effect at high heating rate, the minimum heat required for depolymerisation is reached at higher temperature because of the less effective heat transfer than the low heating rate does.
Hemicellulose started decomposing at a lower temperature but the temperature range on decomposition was wider than did cellulose.
Hemicellulose has the highest reactivity for thermal decomposition because its structure is random and amorphous with less strength. In contrast, cellulose is a crystalline, long chain polymer of glucose units without any branches supporting the hydrogen bonding. Thus, more energy is required for depolymerisation of cellulose polymer as the main mass loss stage of cellulose comes later than that of hemicellulose.
Lignin has heavily cross-linked structure of three basic kinds of benzene-propane units. Hence, the structure of lignin results in high thermal stability and is difficult to decompose. Volatiles produced from lignin occurred from the breaking down of different functional groups with different thermal stabilities. This difference leaded to a broad range of decomposition in lignin [].
Alkali lignin had a high ash content which influences its pyrolytic behaviour. This difference is influenced from their different chemical structures. The thermal decomposition characters of each sample can explain the multi-step decomposition in biomass.
Characteristics of these basic materials influence the mechanisms and kinetics of biomass decomposition. To understand the very complex pyrolytic behaviour of biomass, those of cellulose, hemicellulose and lignin are fundamental and important. Further in this present study, these promising representatives of lignocellulosic main components will be used to analyse their formal kinetic parameter of pyrolysis process in Chapter 7.
It is well-established that the main components lignocellulosic biomass are cellulose, hemicelluloses and lignin, while those of algae can be classified simply as protein, carbohydrate and lipid which present at various proportion depending on species, cultivation condition and harvesting process.
For effective utilization of algae in energy industry, more researches on the pyrolytic behaviour and kinetics are required. In this work, Chlorella vulgaris, freshwater green algae, are selected due to its fast growth rate, high environmental tolerance and easy to cultivate. This chapter will give the methods and results on characteristics of Chlorella vulgaris. Proximate, ultimate and mineral analyses, together with main components analysis are presented here. The latter was done using a dual drum dryer GMF Gouda.
Moisture content was calculated from the weight loss and represented water that may be physically present or chemically bound in the biomass. The ash content was determined by burning 1. The fixed carbon content of the test samples was calculated by difference. The heating value of the microalgal sample was determined by microprocessor controlled oxygen Bomb calorimeter Parr Calorimeter with sample weights ranging from 0. All analyses were done in triplicates.
The analysis results in this section are shown in Table 5. Microalgae have high water content after harvesting but they can achieve low moisture content by drying. The dried Chlorella vulgaris used in this study had low moisture content about 5. However the ash content in the microalgae is higher than land crops [] due to the accumulation of inorganic matter from growing medium. This inorganic content can act as catalysts on pyrolysis process as it is well established for terrestrial biomass that the presence of alkali metals affects the mechanism of pyrolysis, pyrolysis oil quality and increase char yields.
The mineral analysis indicated a large quantity of Ca, Na and K. The crude protein figure is obtained by hydrolysis of the algal biomass and estimation of the total nitrogen which results in an overestimation of the true protein content because proteins are not the only source of nitrogen. However, normally protein is the main component of nitrogen fraction. Other protein estimation procedures are the method after Lowry and Biuret method which based on colour reactions with defined protein content without reacting with other nitrogen-containing compounds [61].
Therefore, the mass cultivation of microalgae requires carefully controlled conditions to produce optimal yield. The large-scale cultures are practically maintained outdoor because they have the advantage of available sunlight. These conditions are more appropriate for countries or regions with high solar radiation [61]. As the light source is the limiting factor, the artificial light sources like fluorescent lamps can be used in the pilot scale of microalgal cultivation [77].
For an efficient and economical photo-bioreactor, the selection of a light source as a key design challenge needs to consider both its spectral quality and intensity. The ability to absorb the solar energy of microalgae in mass cultivation is governed by several factors, including cell density, the length of the optical path of the system, the optical properties of the microalgal cells and rate of culture mixing [78]. Carbon dioxide fixation of microalgae is one of important factors for algae cultivation.
Besides microalgae absorb free carbon dioxide from the atmosphere as a carbon source for photosynthesis from atmosphere, they can gain benefit from the fixation of CO2 in discharge gases from industries and power plants [79]. Normally the ability of diffusion rate of CO2 from the air into the water is too slow to replace the CO2 assimilated by rapidly growing algae.
Thus, the additional CO2 must be applied to cultivation medium to ensure satisfactory growth [80]. Nutrients are another factor for natural growth of microalgae. The main nutrients are nitrogen, phosphorus, and also minor nutrients as silicon, potassium, sodium, iron, magnesium, calcium and some trace elements such as copper, manganese, zinc [50]. After carbon, nitrogen is the most important nutrient contributing to the biomass production.
Some algae can fix nitrogen from the air in the form of nitrogen oxides [81]. Under nitrogen limitation or starvation, there is the discolouration of the cells because the decrease in chlorophylls and the increase in carotenoids, also there is the accumulation of organic carbon compounds such as lipids and carbohydrates depending on the algae species [83, 84]. Although phosphorus in algal biomass is in small amount, it plays an important role as a growth limiting factor.
Three main designs of mass cultivation of algae can be classified as the open system, the closed system and co-process system utilising the carbon source from industrial waste.
The carbon dioxide fixation is mainly from the atmosphere but an external CO2 supply can be installed to enhance the productivity. The advantages of open ponds over closed system are that they are easily to construct and are low cost. Also, they need less energy supply by using natural light energy from the sun [86]. However, open ponds have some limitations which influence the production. The low CO2 diffusion, poor light utilization, and inefficient mixing cause lower productivity compared to the closed system.
Moreover, due to the possibility of contamination or pollution from other algae and heterotrophs in open pond, suitable algal species should able to grow under highly selective environments [87].
The photo-bioreactor Fig. For indoor closed system, the artificial light sources are chosen at a suitable intensity. Co-process with waste treatment This system is to combine the algal cultivation with the carbon dioxide emission mitigation and wastewater treatments. The major driving forces of these designs are the removal of CO2 from the atmosphere, capturing or utilizing the CO2 from fossil fuel combustion, and reducing the cost of nutrients.
This algal biomass can be converted efficiently into biofuels with high productivity and low-cost cultivation [90]. While the CO2 fixation from the atmosphere is limited by low CO2 concentration in air, the mitigation of CO2 emissions from power plants achieves higher yield because of the higher CO2 concentration [91]. The benefits from utilizing waste water treatment process to algae production are the saving of nutrients cost and the minimizing of the freshwater use for algae cultivation.
Some preliminary growth studies indicated both fresh water and marine algae have a potential in waste waters treatment [92, 93]. Microalgae have potential to remove nitrogen, phosphorus, and metal ions from wastewater [79] and CO2 from industrial exhaust gases; however these applications can only be achieved with a limited range of algae which are tolerant of the extreme conditions.
It is difficult to directly compare the performance characteristics of each mass cultivation system because they have different advantages and disadvantages. The choice of system depends on the production costs, value of the desired products, location and production quantity. Hence, the production yield of microalgae is higher in comparison to terrestrial plants [95]. Thus, they can be produced all year round [97]. Figure 2.
Biodiesel from algae oil has main characteristics quite similar to petroleum diesel [98]. Therefore, they do not compete with food production [97]. This process demonstrates an improved method for thermal conversion of ash-rich biomass as microalgal biomass and this process also presents the combination of microalgae into the bioenergy area effectively.
It is the integration of different processes such as algal biomass production, biogas units, pyrolysis processes, gasification processes and heat and power generation plants. Pyrolysis vapours are high quality and highly energetic, dust and tar free which are suitable to combine with heat and power CHP use after a gasification step.
Char produced from intermediate pyrolysis in BtVB process is suitable for further applications such as combustion, carbon sequestration and soil re-fertilisation. The varied sized feedstock can be applied into intermediate pyrolysis; char can be separated from vapour easily.
Moreover, various types of biomass may be introduced to this process. Ash- rich biomass, like microalgae, is also possible for use in the intermediate reactor. Exhaust gases from biogas plants and from gas engines are transferred to algae plantation as a fertilizer.
Apart from the raw microalgae biomass, algae with high oil content can be extracted by mechanical or solvent extraction for biodiesel production. Although microalgae biomass is main feed, other regional feedstocks can be used together with algae during the winter time, when algae production slows down. The BtVB process offers closed loops of fertiliser recycling. Residues from the biogas units may be used as a fertilizer in algae plantation. The high ash content microalgae are processed through thermal conversion techniques and yielded a by-product with high ash content solid phase.
The mineral matter in pyrolysis char is used for the energy crops as fertilizer and at least part of char may be extracted with water to recover mineral elements such as potassium, phosphates, nitrates and silica and then feed this mineral solution into microalgae cultivation system as a growth fertilizer.
Moreover, the aqueous phase of two-phase liquid products which is rich in inorganic matter may be added as a fertilizer to algae plantation and it can be considered as the closed water loop as well. In addition, the exhausts gases from engines are taken to algae medium as another source of fertilizer. Chlorella vulgaris have a simple life cycle with high reproductively rate.
Their cells are divided into two or four non-motile daughter cells and enclosed for a little while within the parent cell wall [].
When the parent cell wall breaks, daughter cells are released into the medium. For decades, Chlorella vulgaris has been widely available in the food industry. They also show great potential for bioenergy applications due to their high growth rate and high oil content. They can be cultured under autotrophic and heterotrophic conditions []. The carbon dioxide concentration, nitrogen depletion, harvesting time, and also the method of extraction are the influences to the lipid content and the lipid compositions.
The lipid content in Chlorella vulgaris increases when the nitrogen concentration decreases and the CO2 concentration increases [73, ]. These proposed bio-sorption potentials of Chlorella vulgaris lead to their biomass production for biofuels combined with wastewater treatment as well as their solvent tolerance, acid tolerance and high CO2 concentration tolerance [] support their application to water treatments and CO2 fixation. It mainly consists of combustion, gasification, and pyrolysis process.
Each gives a different range of products and uses different equipment configurations operating in different conditions. Combustion process is well-defined technology and generates environmental concerns. Pyrolysis becomes an interesting conversion technology because its efficient energy production, easily stored and transported products in the forms of liquid fuels and solid char, and the wide range of produced chemicals [43].
Pyrolysis is thermal degradation in the absence of oxygen and it is a fundamental step in combustion and gasification followed by total or partial oxidation of the primary products. High temperatures and long residence times are suitable for gas formation. The carbonisation process at low temperature and long residence times are the preferred conditions for char formation, whereas pyrolysis promoting the liquid production occurs at medium temperature with short residence times [].
Based on the operating conditions, the pyrolysis can practically be divided roughly into three groups as conventional pyrolysis or slow pyrolysis, intermediate pyrolysis, and fast pyrolysis. The key parameter classifying them is the residence time of solid phase within the reactor. Gas phase residence time for fast and intermediate pyrolysis is kept below two seconds. The proportion of gas, liquid and char products are controlled by the heating temperature and vapour residence times.
The process parameters as well as heating rate also influence the subsequent behaviour of the products by secondary reactions.
Conventional or slow pyrolysis is characterized by a slow heating rate which leads to significant portions of solid product. The residence time may last longer up to days at low temperature for producing charcoal or char mainly and is referred to a carbonization [33].
The characteristics of fast pyrolysis which are described by Bridgwater, et al. Chemical reaction kinetics, heat and mass transfer processes and phase transition play important roles in this complex conversion.
If the purpose of the pyrolysis process is to obtain high yield of liquid products, a fast pyrolysis is recommended. However the fast pyrolytic liquid products present in one phase include water, acids and tars. In the case of non-woody biomass grasses, straws, industrial residues, and agricultural residues , their pyrolysis process and products are far more complicated than those of woody biomass.
In addition, feedstock has to be well prepared with low moisture content. To minimize the exposure period at low temperature, the fast pyrolysis technique uses small particle biomass in a fluidized bed and a very quick heating at the surface of the particle in ablative reactor [].
These lead to the difficulties for separation solid phase from liquid and gas phases. The importance of char transporting with the outer screw as a heat carrier is to improve heat transfer and char also acts as a reforming agent during pyrolysis process. The figure 2. They also proposed the advantages of intermediate pyrolysis process in [, , ] that: 1 Its operating conditions preventing the formation of high molecular tars and offer dry char which is suitable for fertilisation or combustion further applications.
The removal water from the pyrolysis liquids is easy and end up with low water content oily phase. It is suitable for various feedstocks with different optimal residence time. The vapour phase from intermediate pyrolytic reactor has low ash content without dependence on ash content of starting biomass.
This advantage offers the suitability of combining with a gasifier and also the applicability for ash-rich biomass such as microalgae biomass. Furthermore, the internal pressure in this reactor is above atmospheric pressure, typically at least 50 or mbar over atmospheric pressure. This allows pumping pyrolytic vapour effectively into the gasifier. However, basically the reaction products are often lumped into three groups: gas, pyrolytic liquid and char [] or into two groups: volatile and char.
The weight loss of thermogravimetric analysis results from the overlapping of several reactions, thus they can be used for global mechanisms. The reaction mechanisms may be defined in three reactions which are 1 the primary pyrolysis or biomass devolatilization which is the main reaction to convert solid into permanent gas, condensable vapour and char; 2 secondary gas phase reaction of the release gas and tar species; and 3 heterogeneous reactions between solid and gas [].
Moreover, typically the decomposition of lignocellulosic materials may be evaluated by two different models. The first approach is to consider separated competitive reactions to describe the product distribution independent of the chemical compositions [].
Each component decomposes at different rates and by different mechanisms. The volatile products from pyrolysis of biomass are mainly from the degradation of cellulose and hemicelluloses but lignin products dominate char yield []. When the heating rate increases, the weight loss region of each component will be merged to each other and shift to higher temperature. At fast heating rate or high temperature, all component degradation occurs simultaneously.
In addition, the thermal behaviour of each component cannot be applied directly to biomass due to the difference of separation procedure, the presence of mineral matter, and component interaction. Hosaya, et al. There were the significant interactions between cellulose and lignin. Lignin inhibited the thermal polymerization of levoglucosan but enhanced the formation of smaller molecules from cellulose. While cellulose reduced the secondary char formation from lignin and enhanced some lignin-derived product.
On the other hand, the interaction between cellulose and hemicelluloses was described as a weak interaction. Secondary reactions of primary tar vapours become active at high temperatures and sufficient long residence time.
Primary tar is the product from primary pyrolysis and after leaving from the solid phase, the primary tar vapour is subjected to secondary tar reactions []. Tar is a very complex mixture of organic compounds such as phenolics, olefins and polyaromatic hydrocarbon PAH []. Tar formation can occur in the pores of the fuel particle as well as in the vapour phase and on surfaces of the fuel particles or other bed media.
In addition primary volatiles may go through competitive pathways between char formation and cracking to form secondary volatiles []. Van de Velden, et al. Boroson, et al. Main factors which need to be concerned for supporting secondary reactions are particle size, temperature, gas dilution, residence time and amount of fuel [, ]. Although there is numerous weight loss measurements of biomass pyrolysis, there is a difficulty to compare these results because thermal characteristics depend on the biomass species, the geographical origin, age, operating parameters, and the thermal analysis instrument.
Pyrolysis mechanism of cellulose Extensive studies on cellulose pyrolysis mechanism have been made over the past several decades.
Another pathway is char and gas formation. Mamleev, et al. Thus, the gas formation competes with the char formation. Agrawal [] proposed a modified version of the Broido-Shafizadeh model, assuming that cellulose decomposes into gas, char and tar products.
Although the Broido-Shafizadeh model and its modified models have been widely applied, they do not describe the details of decomposition. Later, the recognition of hydraxyacetaldehyde or glycoaldehyde as a major product led to the extension in detail of the cellulose mechanism [, ]. Recently, cellulose decomposition models have been suggested to be more complicated pathways. Banyasz, et al. This model consists of two main pathways low temperature and high temperature pathway.
Hydroxyacetaldehyde, formaldehyde and CO formation are token place at high temperature pathway involving an intermediate. While the formation of levoglucosan or tar at the low temperature pathway is reversible process. Pyrolysis mechanism of Hemicellulose Compared to cellulose studies, there are considerably fewer papers dealing with the decomposition of the various hemicellulosic materials.
Due to the observed multi-peak of the derivative of the thermogram of hemicellulose decomposition, a three successive reaction chain model [27], a successive reactions model [], and a semi-global reaction mechanism model [] were proposed to describe the hemicellulose mechanism see figure 2. From figure 2. The first stage is much faster than the second stage and the reaction time of these two stages decrease with temperature; while their ratio remains almost constant [].
A large fraction of volatiles is produced in the first step due to the cleavage of the glycosidic bonds and the decomposition of side-chain structure. While the second slow degradation may be attributed to fragmentation of other depolymerised units [].
Pyrolysis mechanism of Lignin Due to the complexity of lignin and the difficulty in extraction, the study of pyrolysis mechanism of lignin is limited. Lignin pyrolysis is a radical process of the competition between initiation, propagation and termination reactions.
The initiation reactions are strongly related to the bond energies of lignin structure. While the termination reactions need to be concerned the diffusive limitations to the effective radical collisions and recombinations [44].
Main products from lignin pyrolysis are phenol and its derivatives—methoxyphenol, guaiacol and cresol. Also, methanol, formaldehyde, acetaldehyde, acetic acid and light hydrocarbons, as well as CO, CO2 and H2O are produced from pyrolysis of lignin [].
The primary tar can occur the secondary cracking at the unsaturated side-chain and phenolic aromatic ring structure [] to produce CO, CH4, C2H4 and other light gaseous products [].
Both gauiacols and catechols can undergo secondary reactions with relatively independent of the presence of other molecular species and the residual polymeric material [, ]. Sharma, et al. The yield and characteristics of lignin chars depend on the pyrolysis conditions. The presence of inorganic matter, such as Na and K, lead to high char yield.
As the pyrolysis temperature increases, the aromaticity and the carbonaceous mature of the char increases and hydrogen, as well as oxygen content of the char decrease. These products from the pyrolysis process can be used more readily and may be considerably more valuable than raw biomass. The primary products can be used directly or can be converted further into even higher quality and valuable fuel or chemical products.
The compositions and properties of the biomass-derived products depend on the pyrolysis conditions, i. Liquid products The present interest in liquid products from pyrolysis or other thermochemical conversion are driven by their high energy density which reduces the cost of storage and transport and their potential for further applications of heat and electricity generation and upgrading to premium-grade fuels.
The dark brown organic liquids from pyrolysis are called bio-oil, pyrolysis oils, bio-crude oil, wood oil, pyrolysis liquids, wood liquids, or wood distillates. The pyrolysis oil is composed of a very complex mixture of both aliphatic and aromatic hydrocarbons together with high amount of oxygenated hydrocarbon [, ]. Five broad categories of hydrocarbons detected in pyrolysis oil are hydroxyaldehydes, hydroxyketones, sugars and dehydrosugars, carboxylic acids, and phenolic compounds [33].
The complexity arises from the degradation of lignin which gives a broad spectrum of phenolic compounds. The properties of pyrolysis oil, such as poor volatility, high viscosity, coking, and corrosiveness are still the problems for using with the existing petroleum equipment and particularly in storage, there are some problems about phase separation, polymerization and corrosion of containers []. The presence of a high content of oxygenated compounds in pyrolysis oil results in decreasing heating value, increasing uptake of water in the fuel, increasing the corrosiveness from acidic compounds [, ].
The moisture content of pyrolysis oil which is contributed from free water in original biomass and as a product of dehydration is much higher than that of fuel oil. This high water content causes the low heating value and affects viscosity and acidity as well as leading to phase separation and could affect subsequent upgrading processes. To enable pyrolysis oil for industrial applications, the feedstock selection, pre-treatment, the improvement of pyrolysis unit, the upgrading of oil, the material selection and the ability to blend with other fuels should be taken into account [, ].
Solid products Bio-char is a pyrolytic product which is a carbon-rich solid with some hydrogen and oxygen, and also alkali and alkaline earth matter. The operating conditions at a low temperature and low heating rate, the increasing particle size of the sample and the higher lignin content are promote the higher bio char yield []. Char can be activated by partial gasification with steam or CO2 to increase their porosity or by chemical activation with zinc chloride or phosphoric acid []. When the pore structure and surface area of char are appropriate, they can be prepared for activated carbon applications.
Activated carbon is widely used as an adsorbent in many applications such as toxic metal removal from water [], taste- and odour-causing compound removal [], removal or reduction of gaseous pollutants from the exhaust gas and removal of volatile organic compounds []. Besides absorbent applications, char can be used for catalyst support and base material for fertilizers [] Gaseous products The main gases produced from pyrolysis are carbon monoxide, carbon dioxide and water.
Other products are methane, ethylene, ethane, propylene, propane and methanol. The product yields and gas composition depend on temperature, residence time, and heating rate [].
However, most of bio gas production is focused on the gasification process whose operating conditions support gas formation. The gaseous products with a low to medium heating value can be utilized into a combined heat and power CHP to produce electricity. Moreover, they can be upgraded to higher-value products such as methanol or gasoline but the conversion by gasification is more efficient.
The study relates to following a reaction as a function of time with a suitable analytical technique by measuring the concentration of reactant or product during the progress of the reaction. The aims of chemical kinetics are not only to predict the rate of reaction from a function of state variables, but also to investigate reaction mechanism []. For benefits to industries, the kinetic data of the main reactions have been used for plant design since the reaction rates control the productivity, the cost of the product, and the profit of the plant [].
During a chemical reaction, the concentration of reactants and products change in time. This relationship is based simply on the results of observation and experiment. The powers in the concentration terms of equation above are called the partial orders of reaction. While the overall order of reaction or reaction order n is defined as the sum of p and q.
Since Arrhenius discovered empirically that the rate constant is depending on temperature, the Arrhenius equation has been applied for kinetic studies []. It is referred to a group of techniques in which some physical properties of the sample are continuously measured as a function of temperature, whilst the sample is subjected to a controlled temperature change. By the nature of thermal analysis, the reactions are almost invariably heterogeneous reactions involving at least one initially solid reactant.
For heterogeneous reaction, the concept of concentration of reactants or products does not play the significant role that it does in homogeneous reactions. Moreover thermal degradation kinetics of biomass can be carried out experimentally under either non-isothermal dynamic or isothermal static conditions [].
These different conditions are achieved by the controlled reaction temperature. In the non-isothermal analysis, biomass samples are heated with time according to an assigned heating rate. On the other hand, under static analysis, the experiments are carried on at constant temperatures.
Practically the measurement is either under very slow heating rate to prevent from the gradients of temperature, or under a condition of very fast external heat transfer rates []. The measurement at high heating rate reduces the non-isothermal stage of heating-up phase but it is affected from heat transfer limitations when the sample temperature is not controlled accurately.
In the case of a slow-heating experiment, the weight loss during heating period cannot be neglected. Isothermal measurements have several advantages in kinetic studies [28], which are: i changes in the mechanism are relatively easy to detect because decomposition rates are obtained for a single temperature and therefore a change in the order of reaction can be determined; ii the rate is possible to be calculated analytically; iii temperature of sample is exactly defined after attaining the isothermal temperature, the homogeneous sample temperature is reached [].
However, some disadvantages of isothermal measurements need to be considered. Isothermal analysis requires a larger amount of sample for several experiments at varied reaction temperatures than that of non-isothermal measurement.
This leads to the varied properties of sample [28]. In addition, during heating up period to reach a desired constant temperature, uncertainty arising from decomposition could occur.
Due to the drawbacks of isothermal measurements, non-isothermal or so-called dynamic measurements have been applied to kinetic studies. In addition, one measurement under non-isothermal conditions can give the data in a desired temperature range and it can be calculated to kinetic results quickly. However the non-stationary heat conduction causes the temperature gradient in the sample.
The difficulties to determine the real sample temperature in non-isothermal measurement influence the accuracy in formal kinetic parameters evaluation [28, 29]. Also, it is difficult to maintain the high heating rates that are achieved in pyrolysis reactor. In the last few decades non-isothermal methods have received more attention than isothermal methods.
The main argument in favour of non-isothermal kinetic measurements compared with isothermal kinetic studies is their rapidity [32]. For fundamental studies, it was suggested that the non-isothermal kinetic data should be compared with the isothermal kinetic data for more accurate results [28]. The isothermal experiments are possible to separate unequivocally the temperature-dependent and concentration-dependent parts of a rate expression by experiments in which temperature and concentration are changing simultaneously.
To enhance the ability of isothermal analysis, the improvement of measurement apparatus to overcome the drawbacks of isothermal method need to be considered. Hence, substituting equation 3. They can be classified roughly into the differential method and the integral method. Work hour units for joints include handling, cutting, deburring and soldering. Each type represents a series of sizes with different wall thicknesses.
The pipe weight per LF above is Type K. The selection of solder depends primarily on the operating pressure and temperature of the system. The tin-lead solder is suitable for moderate pressures and temperatures. For higher pressures, or where greater joint strength is required, tin-antimony solder can be used. Corrugated Metal Pipe is produced from uncoated steel, galvanized steel, or aluminum coiled strip ranging from 18 gauge 0.
The pipe weight per LF above is based on 8 gauge 6. This pipe is used for such applications as water drainage, flood control, storm sewers, concrete piling shells and culverts.
Work hour units for joints include handling, cutting, heating and butt-fusion. Each SDR has its own pressure rating identification. The SDR system is a specific ratio of the nominal outside diameter to the minimum specified wall thickness. Each classification represents a series of sizes with different wall thicknesses. Work hour units for threaded joints include handling, cutting, threading and joint make-on.
Work hour units for fusion joints include handling, cutting, heating and thermo-seal fusion. Polypropylene Pipe is a polyolefin that is lightweight and generally high in chemical resistance.
Its weight per LF can vary higher than polypropylene but the work hour units above will apply to this material also. Work hour units for solvent cement joints include handling, cutting and joint make-on. Poly Vinyl Chloride PVC Pipe is characterized by high physical properties and resistance to corrosion and chemical attack by acids, alkalis, salt solutions and many other chemicals.
It is attacked, however, by polar solvents such as ketones, some chlorinated hydrocarbons and aromatics. Its weight per LF can vary slightly higher than PVC but the work hour units above will apply to this material also. Work hour units for epoxy cement joints include handling, cutting and joint make-on. Work hour units for butt wrap joints include handling, cutting and glass matte overlay. The resin systems vary from isophthalic polyesters and epoxy vinyl esters to specialty resins for custom applications.
The glass reinforcement includes filament rovings and unidirectional and bi-directional woven products. FRP pipe is available in either lightweight or extra- heavy wall. The pipe weight per LF above is extra-heavy. Work hour units include installation of gasket. For Orifice Flange Sets, multiply standard units by 2.
For bolt-ups to an existing flange or equipment nozzle, multiply standard units by 2. See section B. Work hour units for Buttweld End valves are for handling only and do not include the required buttweld. If material is alloy, see section B. Work hour units for Flanged End valves include handling and applicable time for mating valve flange to line flange; to equipment nozzle; or to another valve flange.
For applicable line flange unit work hours, see section D. Work hour units for Bolt-Through Type valves are for handling only and do not include the required mating flange bolt-ups.
See section D. Work hour units are for handling only and do not include the required joint connections. See the appropriate section for applicable unit work hours. For applicable installation details, see Fluor Daniel Standard Assemblies.
All work hour units represent outdoor installation. For indoor applications, make adjustments as necessary per specific project. Any supports required are not included.
For field installation of high voltage bushings, radiators, fans, etc. If some items are shipped attached to transformer, adjust percentage accordingly. If transformer is shipped with oil, without high voltage bushings, radiators, fans, etc. If transformer is shipped complete with oil and components attached, use standard units as shown. For any activities which are not included in this section, see Means, Richardson, NECA or other recognized estimating publications.
All work hour units represent indoor installation. For bolting section together, if required, add 1 WH per section. For checkout and tighten internal connections, if required, add 1 WH per section. All work hour units represent NEMA 1 classification, unless otherwise noted. Any substation structural steel required is not included. Work hour units include setting generator in place, controls connected, batteries and charger installed. Work hour units do not include exhaust system piping, fuel piping, underground fuel tank, additional cooling system, remote alarm annunciator, etc.
Conduit units exclude bends factory or field , terminations and supports. Labor units for factory bends are added into the estimate the same as conduit fittings.
Labor units for field bends are in addition to the linear conduit quantity. The actual bend is part of the conduit quantity, only labor is added. Conduit units exclude bends factory or field and supports. Or Vert. Use same units for all other items. Units shown include lugs and hardware. Cable Terminator for Class I — Div. II includes seal. Supports not included. Fixture work hours include lamp. For wood pole setting, see Pole Line section.
Post-mounted landscape fixtures do not include the post. The above Cadweld connection units include mold, mold handles and charge. The above bare copper wire units are for installation in a trench only.
The above bare copper wire units reflect the main grounding electrode system. Where short runs are required the units must be increased. Also increase units for grounding installed other than in trench, i. Per Approx. Of 1, O. For wire and terminations, see applicable section. Installation units include hauling up to two 2 miles.
Above units include necessary brackets and fasteners to mount transformers to existing pole. N-Haz unit — Cable with Jacket only. Div-2 1 unit — Cable with Jacket and Shield. Div-2 2 unit — Cable with Jacket, Shield and Jacket. ANODE 8 55 2. ANODE 8 90 2. ANODE 8 3. ANODE 8 4. All Anode work hours are based on typical installation at or near the surface. For deep groundbed installation add work hours as required by depth.
See Means, Richardson or other recognized estimating publications. For Cadweld Connections: Cable-to-Cable, use 3. Cable-to-Pipe, use 3. MM SQ. Transducer 4. Indicating Switch 4. Safety Element Rupt. Disc 2. Gauge 3. Or Pneu. All work hour units in the Install column include unload, storage, specification verification, handling to erection site and installation of device, unless otherwise indicated by note 6. All other activities for the Install column see note 1 are included in the Control Systems account section These installation hours are for individually shipped components.
Typically these devices are furnished pre-mounted to an associated Control Valve, therefore no installation labor is required. To verify installation requirements, consult Control Systems lead engineer.
For any activities that are not included in this section, see Means, Richardson or other recognized estimating publications. Panel mounted devices are typically pre-installed by the panel vendor, therefore no installation labor is required. If installation is required, see note 2. All work hour units in the Install column include unload, storage, handling to erection site, panel cutout and installation of device. Threaded fittings for Air Supply Bulks include handling, cutting, threading and joint make-up.
Work hour units per LF for Tubing are for wall thickness up to and including 0. For heavier wall tubing, increase work hour units proportionally. Tubing fittings for Process Bulks include handling, cutting, deburring and joint make-up.
Any additional supports required are not included. For Non-Fireproofed column, use 4. SP Near White Blast Cleaning Blast cleaning nearly to white metal cleanliness until at least 95 percent of each element of surface area is free of all visible residues for high humidity chemical atmosphere where high cost of cleaning is warranted.
SP-5 White Metal Blast Cleaning Removal of all visible rust, mill scale, paint, and foreign matter by blast cleaning by wheel or mozzle dry or wet using sand, grit, or shot for very corrosive atmosphere where high cost of cleaning is warranted. There are no averages that apply. For a comprehensive listing of square feet per lineal foot for various structural shapes and sizes, see Richardson.
The LIGHT structural steel category includes flange, channel, tee and angle shapes; ladders; cages; plate; grating; and other miscellaneous steel items. Pipe diameter to square feet conversion based on pipe O. Vessel square footage calculation: Shell: greatest circumference times straight length or height Elliptical heads noncircular — most common is a ratio : greatest diameter squared squaring provides coverage for the elliptical shape Hemispherical heads circular : diameter squared times pi 3.
For removal of paint coatings, multiply the appropriate work hour unit above times 3. Disposal of material generated during the removal process is not included.
Field painting is typically a subcontract item. Applications below minus degrees F are termed cryogenic; those above degrees F are termed refractory; these categories are not included in these work hour units. The use of insulation materials to absorb noise emitted from piping and equipment is classified as noise abatement; this application is not included in these work hour units.
The use of whole sizes for HOT and half sizes for COLD was done intentionally to emphasize the differences between their respective applications. For any thickness required that is not listed, simply use the midpoint between the lower and higher thickness columns.
For all types of HOT Pipe insulation Glass Fiber, Mineral Wool and Calcium Silicate , the work hour units are based on the following erection method: Pipe cover is secured with gage wire on 9-inch centers. For all types of COLD Pipe insulation Cellular Glass and Polyurethane , the work hour units are based on the following erection method: Joints are buttered with joint sealer.
Pipe cover is secured with fiberglass tape on piping 4 inches OD Outside Diameter and smaller spaced on 9-inch centers. For all types of HOT Equipment insulation Glass Fiber, Mineral Wool and Calcium Silicate , the work hour units are based on the following erection method: Shell cover blanket or block is applied with staggered joint arrangement.
Top and bottom edges are securely tied over support rings with wire on inch centers. Vertical and horizontal seams are laced together by interlocking the wire mesh and with wire ties where necessary. The insulation is secured in place with bands spaced on inch centers. Head cover is shaped so that all sections closely fit the contour of the head and are laced together with wire, or are secured with bands on inch centers at tangent line.
Unexposed head cover is secured with wire to insulation supports provided by the vessel manufacturer. Weatherproof jacket on vertical equipment is supported on S-clips spaced on 4-foot centers. The jacketing for vertical and horizontal equipment is secured with bands spaced on inch centers with one band at each circumferential lap. On vertical equipment, band loops are included on each band to prevent vertical movement.
For all types of COLD Equipment insulation Cellular Glass and Polyurethane , the work hour units are based on the following erection method: Shell cover block is applied with staggered joint arrangement. Joints are buttered with joint sealer. In double layer applications, the inner layer is applied without joint sealer. Each layer is secured with bands on inch centers. Outer layer joints are offset from inner layer joints.
Vapor barrier is outer layer only. Joints are sealed with a foil-to-mylar 3-inch wide strip applied over the vapor barrier. Head cover is shaped so that all sections closely fit the contour of the head. Site treatments. Circumstances of site discovery. The higher frequencies of iron-working sites in Chad, or by intentional backfilling of the construction and of grinding hollows and lithic sites in Cameroon, trench. Different site evaluation practises account for are particularly noteworthy.
These may in part reflect most of the greater proportion of sites excavated in real differences in prehistoric activities along the pipe- Chad compared to Cameroon. Excavations have taken line route, but the larger number of relatively older place on 32 sites in Cameroon and to the beginning lithic sites in Cameroon may also be a reflection of dif- of on 39 sites in Chad. In some cases, these ex- ferent erosional contexts.
In Chad, most of the area cavations consisted of small test pits: in other cases, surveyed consisted of flat plain mantled with relatively they were substantially larger. Table 2 Cameroon Tab. These treatments varied according to compared to the savanna-forest mosaic and tropical the characteristics of the sites. Monitoring during con- forest regions to the south, but also appears to reflect struction was applied to medium-priority sites when real increases in site densities in the deciduous further treatment was not deemed to be necessary, wooded savanna.
Chadian site densities are not di- given information available at the time of discovery. In rectly comparable to those in Cameroon, since the fig- some cases, monitoring resulted in a site being ures for the former country include sites located dur- redesignated as high priority, with further treatment ing pre-construction survey in the OFDA, as well as applied.
In particular cases, impacts to sites could be sites found along surveyed roads in Chad. Sites lo- limited by narrowing the right-of-way around the site cated during road surveys are not yet included in Journal of African Archaeology Vol. Estimated ages of sites, at time of site discovery. Cameroonian totals. The difference in site density is, Stone Age, Neolithic and Iron Age — to categorise however, still significant when only savanna and for- sites located in the course of the CEP archaeological est zones in Cameroon are compared, thus avoiding programme.
It is also the reason for some overlap in the age Also notable are a number of regions where site categories in use see Tab. Many of the sites located densities are considerably reduced Fig. Not all are at present unknown, but may well be different for Iron Age sites yield evidence of iron working, and each area.
Along the pipeline right-of-way in Chad, such sites can be difficult to distinguish from Neolithic distinct clustering of sites on a smaller scale is asso- occurrences, especially when lithics and iron-working ciated with proximity to rivers and areas where iron are sometimes found in association. Approximately working takes place see below. Very little material potential mixing of assemblages from multi-compo- from this period — years ago has been lo- nent sites, the typologies use to date these sites were cated in southern Cameroon, and the material basis of fairly basic and our initial estimates of site ages in this phenomenon obviously requires further study.
In many cases approximate. In the long run, it is unlikely that Journal of African Archaeology Vol. However, data recovered in this project hunting and gathering to farming in the tropical forest may indicate that this early phase of the phenomenon of southern Cameroon. One element that dated to approximately bp.
Project excavations on must be considered in the examination of this move- the site of ECA Ndtoua Rock Shelter have yielded ment is the introduction of iron technology into the a similar date in the lower part of the stratigraphy, region, together with the attendant replacement of which in total provides initial data for the construction stone tools.
None of the pit sites found along the pipe- of a chronocultural sequence for this area. These early sites were most and excavation was undertaken in that area of sedi- commonly encountered in erosional contexts on hill- ment accumulation. We hope that, in future, the Chadian and Cameroonian The Shum Laka site in the Grassfields area of archaeologists that have been involved in this project Northwest Province in Cameroon also yielded a will have the opportunity to further investigate some macrolithic stone tool assemblage of mid-Holocene of the sites that they have had a hand in locating.
At date LAVACHERY , but with basalt as the prevalent this point, however, a number of issues raised by this raw material and, more importantly, a polished stone research have already proven particularly interesting, tool component and pottery. The ceramics and pol- and deserve to be discussed in somewhat more detail.
For location, see Fig. These data, as well about bp at the latter site. More data on subsistence systems would discovered until now primarily on sites in the area of course be required to confirm this possibility. Excavations at Shum Laka debris, including ceramics, iron and slag in some cases LAVACHERY show a similar persistence and rare lithics and faunal remains including of lithics associated with iron objects and ceramics ovicaprids , as well as charred incense tree Canarium until at least bp.
On the island of Bioko, use of schweinfurthii pericarps and oil palm Elaeis stone tools persisted until the arrival of the first Euro- guineensis nuts, and possibly Pennisetum. On previ- peans. This combination of artefact types may also in- ously excavated sites, pits appear in large numbers dicate the persistence of forager lifeways alongside more than at Nkometou, approximately 30 at Nkang agricultural activities, possibly paralleling more recent [ESSOMBA ; MBIDA b] , and indeed are the relations between Pygmy and farming populations.
Radiocarbon dates from selected sites noted in the text. All dates are on charcoal unless otherwise noted. Sites with pits along the pipeline route. There has been some debate about the uses of tions for East and Central Africa, since it indicates dif- these pits.
Researchers have posited a primary storage fusion of this crop across the Indian Ocean and across function for these features, with refuse disposal as an Africa at least — years earlier than previ- additional function when such storage had ended, but ously thought.
There is evidence that in at least some cases such pits were In the course of fieldwork along the pipeline used as wells or latrines MBIDA , while pits right-of-way, these pit features have been located on on Gabonese sites in similar contexts appear to have 29 sites in the forest zone of Cameroon, from east of been used as quarries for clay used in house construc- Nanga Eboko to the Atlantic coast at Kribi, a consid- tion, and were thereafter filled quite quickly Bernard erably wider distribution than had been indicated by Clist, personal communication It is probable earlier discoveries Fig.
Provisional examination of that the pit features found in the course of this survey materials and radiocarbon dates from excavated pits served a variety of different purposes, at different on a number of these sites see for example ECA times during their use cycle. The discovery of banana a ceramic assemblage dominated by walking-comb and phytoliths in southern Cameroon at that period will comb-stamped decoration on pottery, and a second also force a reconsideration of economic reconstruc- set dated to ca bp, where pottery decora- Journal of African Archaeology Vol.
Dates on charcoal recovered from four is characterized by more or less equal percentages of pits at ECA Ndjore indicate occupation over a comb-stamping, walking-comb and stick- and comb- limited time-span around the turn of the second millen- grooving between bp. Further to the north- nium BP, but bone from a human skeleton recovered east, in the Nanga Eboko area, the early pit site of from one of those pits yielded a modern date.
The ECA Zili yielded pottery decorated using those dates recovered from two pits at ECA Ezezang four techniques at bp, while at the later sites of are some centuries apart, although the date from one ECA Meyang and ECA Nanga ceramic pit is in agreement with dates recovered from other ex- decoration is entirely dominated by comb-grooving cavations on that site. There is, on the other hand, between bp. A number of sites with smaller very little overlap in dates from pits at ECA and more recent ca bp pits have also been Bissiang — 2 pits and ECA Meyang — 2 pits , in- discovered in the wooded savanna in southwestern dicating that these pits were dug at different times.
Chad, although their primarily roulette-decorated ce- These results paint a mixed picture, with evidence for ramics do not appear to be closely related to those contemporaneity of multiple pits often some distance found on the southern Cameroonian sites. Pit features apart along the right-of-way at many sites but with are also found on sites considerably north of the for- evidence of occupation over a significant time-span at est zone in Central and West Africa, although, as in others.
In the latter cases, we of course do not know Chad, they are not usually a dominant feature on such whether occupation was continuous over the inter- sites. These pit features represent the most substantial The earliest evidence for iron use in the forest evidence for prehistoric settlement in this region.
The sites probably span the time during which from the Atlantic coast. The nature of set- This is the first iron-processing site to be excavated in tlement associated with these pit sites requires further the tropical forest of Cameroon. The dates recovered research. In the former case, occupation in rela- ess by which iron technology replaced stone tools in tively large villages would be indicated, while the lat- southern Cameroon.
There is evidence than kilometers along the pipeline transect indi- for a considerable range of dates from different pits on cates that significant sedentary communities, probably some of the pit sites previously discovered, while the exploiting domesticated crops and also manipulating results from sites discovered during the course of wild resources including oil palm, were not confined to fieldwork along the pipeline right-of-way are complex.
These settlements were in fact a general Journal of African Archaeology Vol. The very low especially given the correspondence between the dis- density of material distributions in these sites renders tribution of pit feature sites and the modern distribu- only recent examples relatively detectable through sur- tion of Bantu languages in Cameroon.
Occupation of wooded savanna Older, large settlement sites with much higher ar- Primarily dry-season survey work in the wooded tifact densities are present in Chad, but are generally savanna and forest-savanna mosaic zones of encountered in sub-surface contexts.
These sites, with abundant ceramics frequent detection of small surface sites than was the but no real stone industry, show evidence of signifi- case further to the south. Site densities during the cant settlement before the expansion of iron-working monitoring phase of pipeline construction were much ca bp see below.
A different settlement pattern more comparable. Relatively few top features along the edge of the escarpment. This substantial sites were found on poor lateritic soils and area occupies an intervening position between two swampland southwest of Doba in Chad, for example, rather different ecozones, with relatively open plains while habitation sites were more common within two — below and wooded plateau above, and also has a con- three kilometres of the permanent rivers in the re- siderable defensive potential.
Both of these sites have gion. The and other artefacts, sometimes extending over areas of only charcoal samples found on that site dated more more than a kilometer along the pipeline right-of-way. Settlement Iron-working sites in this region was quite mobile during the pre-colonial and colonial periods E. Brown, personal communica- If pit sites are perhaps the most striking archaeo- tion, , with villages being relocated periodically logical occurrences along the southern part of the to take advantage of fresh soils and during more re- pipeline route, iron-working sites are their equivalents cent periods to avoid attack by slave-raiding groups.
A total of 40 iron-working sites Such behaviour can still be seen in the study area to- were found in the course of CEP archaeological field- Journal of African Archaeology Vol. Nkonkonda Fig. Iron-working sites along the pipeline. Sites with small amounts of slag located in the comparatively well-watered area near such sea- on the surface or in excavation units are much more sonal water sources.
There is little evidence for do- common.
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