Sizing, Construction and Experimentation of a Chinese Type

Research Article Volume 8 Issue No.9 Sizing, Construction and Experimentation of a Chinese Type Digester in Mamou Prefecture (Republic of Guinea) Ansoumane SAKOUVOGUI1, Mamadou Foula BARRY2, Younoussa Moussa BALDE3, Cellou KANTE4, Mamby KEITA5 Higher Institute of Technology of Mamou (Guinea Republic) 1, 2, 3 Gamal Abdel Nasser University of Conakry, Teaching and ResearchLaboratory in AppliedEnergetics, (Republic of Guinea) 4, 5

Abstract: This research focuses on the design, construction and testing of a Chinese-style digester fed by cow dung on a family farm in Mamou, Guinea. The monitoring of the following parameters:temperature, pH, pressure, cumulated daily volume of biogas production, has been done. The total volume of the digester is 2.30 m3 with a gasometric portion of 0.35 m3. The analysis of cow dung samples used for the dry matter content (21%), the organic matter content (54%), the carbon content (31%), the moisture content (73%) and pH (7.5). During the 30 days of digestion, the average temperature in the digester is 28.23°C, the pressure of the biogas varies from 0.10 to 12 kPa, the pH of 6.0 to 8.50 and the cumulative production of biogas is 38m3. The product gas was tested by the ignition of a biogas lamp and the measurement of the combustion flame temperature gave 160°C.

Key words: sizing, construction, digester, experimentation, characterization, cow dung

I. INTRODUCTION potential of the country. Livestock is after agriculture, the Methanation is a natural process of biological degradation of second activity of the rural world [7]. The valorization of organic matter in a medium without oxygen (anaerobic these animal droppings could be considered as an economical digestion), due to the action of multiple microorganisms and ecological solution through an energy autonomy and a (bacteria). It takes place in four stages (Hydrolysis, sustainable agricultural development of the rural zones Acidogenesis, Acetogenesis and Methanogenesis), with characterized by a high animal density posing most often different bacteria adapted to each of these stages in a digester difficulties within the farms [8]. that transform complex organic substrates into simple The digester, also called fermentor or anaerobic molecules monomers: acids, alcohols ..., then into biogas [1]. bioreactor, generally consists of a closed, airtight and Biogas is a colorless and flammable gas produced by thermally insulated vessel from the outside in which different anaerobic digestion of animal, plant, human, industrial and microorganisms chemically and biologically degrade organic municipal waste, to give mainly methane (50-70%), carbon wastes and effluents to produce biogas. usually made of dioxide (20 - 40%) and traces of other gases such as Nitrogen, concrete or stainless steel, but its shape varies (round, Hydrogen, Ammonia, Hydrogen Sulfide, Water Vapor, etc. rectangular) etc. according to the manufacturers [9]. [2]. Methane is the main component with a heating value in The fixed dome digester is called "Chinese type", for the range of 21 to 24 MJ/m3 (6 kWh/m3) [3]. The temperature having been built for the first time in Jiangsu (China), in 1936, of the combustion flame of the biogas is a function of its it has a constant volume. This type of digester is the most methane content, it is between 800°C and 1100°C [4]. widespread in the rural world, with more than 5 million Biogas production systems have several advantages, family-size units in China at the end of the 20th century. The such as: elimination of greenhouse gases, reduction of odors, size of these types of digesters depends on the location, the organic fertilizer production, heat and electricity production number of households and the amount of substrate available. [2]. Generally, the optimal production of biogas depends on Their volumes generally vary between 4 and 20 m3 in Nepal, 6 the type of digester, the operating conditions and the type of and 10 m3 China, 1 and 150 m3 in India and Nigeria, about 6 organic substrate. The main physico-chemical parameters of m3 for a family of 9 people [10]. anaerobic digestion are: temperature, pH, nutrients and toxic The sizing and construction of a digester is generally or inhibitory compounds. A digester operates in three a function of the main objectives pursued by anaerobic temperature ranges: the psychrophilic range, having a digestion, in relation to the material, technological and temperature below 25ºC, the mesophilic range with a economic resources available [11]. This dimensioning is based temperature ranging between 25 to 40ºC and the thermophilic on data relating to energy consumption (cooking, heat, range with a temperature ranging between 50 to 65ºC [5]. lighting, electricity, etc.) and on initial parameters such as the In general, Africa faces the problem of low energy internal height and diameter of the digester. From these data, consumption, especially in rural areas. Only South Africa the other sizing parameters of the digester (volume and consumes 45% of the total electricity produced in Africa, dimensions of the gasometer, dimensions of the inlet and North Africa consumes 30% and Sub-Saharan Africa outlet of the digester, the thickness of the walls, etc.) will be consumes 24% of the total electricity produced in Africa [6]. calculated [12]. In Guinea, research work on the construction of The aim of this study is the sizing and construction of biodigesters began in 1977 and 1980 with the construction of a Chinese type digester fed by cow dung, in order to follow Indian-type experimental digesters at the Faculty of the evolution of certain parameters such as temperature, pH, Agronomy of Foulaya in Kindia. In general, biomass potential pressure and production kinetics of the cow dung biogas for (agricultural residues, agro-industrial waste, domestic waste, this type of digester. plants and animals) represents 80% of the total energy

International Journal of Engineering Science and Computing, September 2018 18926 http://ijesc.org/ II. MATERIAL AND METHODS same duration, the dry season from November to April and the A. Description of the study area rainy season from May to October, rainfall varies between This study took place in the Mamou prefecture located 270 1600 mm and 2000 mm, with an average annual temperature km from the capital Conakry between 10°22'39.93''N and of 25°C [13]. It covers an area of 8000 km2 with a population 12°5'2.57''W at an average altitude of 700 m, with a climate of 318738 inhabitants (2014) [14]. The map of Mamou characterized by the alternating of dry and rainy seasons of the Prefecture is shown in figure 1.

FIGURE 1 MAP OF THE PREFECTURE OF MAMOU

A. Materials FIGURE 2 DIAGRAM OF THE STUDY DIGESTER During this study, we used several types of equipment depending on the tasks to be performed, namely: sizing, construction and experimentation of the digester. The set of equipment used for the sizing and construction of the digester are: software (Mathcad 2000 Professional and Matlab R2016a), measuring devices for tracing and digging of the digester pit (centimeter, decameter, level, string, wire to lead, pointed wire, wooden ruler, square), work tools for the construction of the biodigester (hoe, cutter, shovel, pickaxe, wheelbarrow, hacksaw, pincer, buckets, drum, hammer, chisel , trowel) and biodigester experiment measuring apparatus a K CHROMEL+ ALUMEL- temperature sensor coupled to a CL3020 multimeter, a LANNENG brand manometer and the 1) Feed tank, 2) Digester «(a) Bottom, (b) Cylindrical part, pH indicator strips of the type (pH- indicator strips). (c) Gasmeter, (d) Gas pipe »,(3) Exit tank of the digestates.

B. Methods Since the volume of the digester to be constructed is known, Dimensioning: the basic design parameters (diameterDc and heightHc of the cylindrical part) of the digester are calculated according to the The Florentino method [11] was used to determine the mathematical model proposed by Florentino [11], it consists geometrical design parameters of the digester. Equations (1) of constrained optimization. With reference to (3). and (2) are used to calculate the volume of construction (VD) π 48.π of the digester and the total volume of substrate (VTS) . D2 . H + . D3 ≥ V (3) including the amount of cow dung (V ) and the volume of 4 c c 3072 c D B water (VE) required for feeding the digester, taking into account the hydraulic retention time (TRH). With the following constraints: 0,5. Dc − Hc ≤ 0 ; 0,6. Dc − Hc ≥ 0 et Dc > 0

VD = VT × TRH (1) Equation (4) is thus used to calculate the volume of the cylindrical portion (Vc) of the digester. VTS = VB + VE (2) π.D2.H V = c c (4) Figure 2 shows the schematic of the constructed digester c 4 model. Equation (5) calculates the volume of the bottom of the digester (VfD).

International Journal of Engineering Science and Computing, September 2018 18927 http://ijesc.org/ 2 π.hf 3.Dc 2 hf 1 biogasstored at this maximum pressure are calculated with VfD = + hf ; Avec : ≥ (5) 6 4 Dc 8 reference to (9) and (10), respectively.

Hc The volume of the gasometer (Vg) iscalculated by (6). Pmax = + hcs (9) 2 3 π .hg 3.Dc 2 hg 1 Vg = + hg ; With : ≥ (6) πD2 H 6 4 Dc 4 V = c . c + V (10) bPmax 4 3 g Equations (7) and (8) show the formulas for calculating the volume of the feed tank (Vca) and the volume of the outlet C. Construction : tank (Vcs) of the digester, of parallelepiped and cylindrical The digester was built from May 11 to June 2, 2017 at the shapes respectively (see figure 2). Higher Institute of Technology (IST) of Mamou, respecting the dimensions calculated by the programs and the different Vca = Les . les . hes (7) equations mentioned above. The main steps are the π .D2 .h followingones for the construction of the digester: site V = cs cs (8) cs 4 selection, dimension tracing, pitdigging, material procurement and clean construction. Figure 3 shows the steps of the The maximum pressure reached by the biogas in the digester construction of the digester. in meters of water column (mCE) and the volume of

FIGURES 3 STEPS IN THE CONSTRUCTION OF THE DIGESTER

a) Laying the first bricks b) Laying pipes

c) ConstDome construction 1) Feed tank, (2) Digester, (3) Digestateoutlet tank

The values of the theoretical and actual design parameters of the constructed digester are given in table I.

TABLE I DIMENSIONS OF THE DIGESTER Settings Value Symbol Unit Calculated Reliable 3 Need for biogas Qb 4,25 4,00 m /d

Diameter of the cylindrical part Dc 1,54 1,50 m

Height of the cylindrical part Hc 1,15 1,00 m

Height of the gasometer part hg 0,38 0,37 m

Digesterbottomheight hf 0,19 0,18 m 3 Volume of the digesterbottom Vf 0,18 0,17 m 3 Volume of the cylindrical part Vc 2,14 1,78 m 3 Volume of the gasometer Vg 0,39 0,35 m 3 Total volume of the digester Vtd 2,70 2,30 m

Length of the inlet tank Les 0,80 0,77 m

Width of the inlet tank les 0,70 0,56 m

Height of the entrance tank hes 0,60 0,62 m 3 Volume of the inlet tank Vca 0,34 0,28 m

Diameter of the outlet tank Dcs 0,50 0,60 m

Outlet tank height hcs 1,00 1,08 m

International Journal of Engineering Science and Computing, September 2018 18928 http://ijesc.org/ 3 Volume of the outlet tank Vcs 0,20 0,30 m

Distance between the inlet tank and the body ded 0,70 0,60 m

Distance betweenoutlet tank and body dsd 0,50 0,30 m

PVC supplyhoselength Lapvc 1,80 1,70 m Angle of inclination of the supply pipe α 45 42 °

PVC outlet pipe length Lspvc 0,50 0,40 m Angle of inclination of the outlet pipe α' 75 72 °

Coverdiameter Dcd 0,35 0,40 m

Maximum biogas pressure in the digester Pmax 12,25 12,00 kPa 3 Volume of biogasstored at Pmax Vb 1,50 1,00 m

The photo of the constructed study digester isillustrated in figure 4.

FIGURE 4 PHOTO OF THE STUDY DIGESTER

(1) Feedtank; (2) Digester; (3) Exit tank of digestates; (5) Gas pipe

The schematicdesign of the entire system installation isshown in figure 5.

FIGURE 5 DIAGRAM OF THE INSTALLATION OF THE METHANIZATION SYSTEM

The names of the different parts of the scheme are given in table II.

TABLE II NAMES OF THE DIFFERENT PARTS OF THE SYSTEM N° Designation N° Designation 1 Digester 13 Valve for fireplace (burner) 2 Feed tank of the digester 14 Lamp valve 3 Digestateoutlet tank 15 Burner 4 Storage tank of the digestate 16 Lamp 5 Digestate 17 Temperaturesensor in the digester 6 Water trap look 18 Temperaturesensor for the inlet tank 7 Galvanized pipe Φ15 19 Temperaturesensor for the outlet tank 8 Galvanizedelbow Φ15 20 Manometer 9 Ball valve 21 Hose Φ8 10 PVC elbow Φ15 22 Water trap 11 PVC hose Φ15 23 Valve for water trap 12 PVC tee Φ15 24 PVC pipe Φ50 International Journal of Engineering Science and Computing, September 2018 18929 http://ijesc.org/ Experimentation of the digester: of dry matter (MS) and organic matter (MO). The volumetric The substrate (cowdung) was collected from the 15th up to method made it possible to determine Organic Carbon (CO) 20th June 2017 on a family cattle farm in the village of according to the French standard NF U 44-161 [15] and Total Dounkaiwal in Mamou. The cow dung samples were Nitrogen (NT) was determined by the Kjeldahl method [16]. analyzed in the Microbiology laboratory of the National The digester was loaded on June 25th, 2017 with 750 kg of Office of Quality Control (ONCQ) of Conakry. The cowdung and 750 liters of water, a ratio of (1:1). Figure 9 gravimetric method was used for the determination of the shows the phases of the digester charge and the temperature following parameters:densities (Mv), humidity (H), quantities measurement.

FIGURE 9 CHARGE AND EXPERIMENTATION OF THE DIGESTER

a) Cow dung b) Charge of the digester c) Temperature measurement

III. RESULTS AND DISCUSSION very close to the results reported by other authors, ie (55%) [17]. The carbon content is 31% and it is in the ranges of The daily value of the forecast biogas requirements carbon contents according the litterature. It promotes the previously fixed at 4.25 m3 per day is close to the actual increase and growth of microorganisms in the substrate. The biogas production value (4m3) of the digester built. Similarly, moisture content is 73%, which is included in the range (60 to the values of the geometrical dimensioning and construction 90%), for the optimal production of biogas. The pH value is parameters of the digester are relatively equal. Thus, the 7.50; this value is in accordance with the standards indicated actual volume of the digesteris 2.30 m3 and the volume of the in the literature for the production of biogas [18]. gasometeris 0.35 m3. The experiment of the digester concerns the measurements of The physicochemical characteristics of cow dung the different parameters: temperature, pressure, pH, daily used in this study are: dry matter content, organic matter production and cumulated daily production‟s. content, carbon content, moisture content and pH. The solids The temperature variation curves in the digester, the ambient content (DM) is 21%, it is relatively higher than that of the medium and the feed tanks for the substrate and the output of literature (15%). The organic matter (OM) content is 54%, the digestates are given in figure 10.

FIGURE 10 CURVES OF TEMPERATURE VARIATION

Figure 10 shows that the temperature variation curves in the to the mesophilic mode of digestion [17]-[19]. The average four (4) media (digester, ambient and inlet and outlet) are temperatures in the supply and outlet tanks are (25.27°C and similar and have the samepaces. The temperature variation 26.17°C) respectively and that of the ambient medium is curve in the digester is above the other three curves of 25.63°C. temperatures. The temperature in the digester varies from The variation in pH during production isgiven in Figure 11. 25°C to 3°C with an average of 28.23°C, which corresponds

International Journal of Engineering Science and Computing, September 2018 18930 http://ijesc.org/ FIGURE 11 pH VARIATION CURVE 9.00

8.00

7.00

6.00

5.00

pH 4.00

3.00

2.00

1.00

0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time of digestion (d)

Figure 11 shows that the pH varies between (7.0 and 8.50) evolution of the slowest pH, it is between the 8th and the 15th with an average of (7.62) which is very favorable to the day of production of the biogas. The pH values go from 6.0 to development of microorganisms for biomethanation. Three 7.50. Phase of stabilization of the pH of the substrate, it is phases are observed in the evolution of the pH values during included from the 15th to the 30thday of production, during the production of biogas [20], which are: Acidification phase this period the values of the pH are between 7.50 and 8.50. of the substrate, it is observed between the beginning of the experiment and the 8thdaywith values from 7.00 to 6.00. The variation of the pressure in the digester and the piping are Alkanisation phase of the substrate, it is the period of given in figure 12.

FIGURE 12 PRESSURE VARIATION CURVE 14.00

12.00

10.00

8.00

6.00 Pressure (kPa) Pressure

4.00

2.00

- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time of digestion (d)

Figure 12 shows that the pressure in the digester varies with to 30thdaytherewas a regression, for a minimum value of 2.16 biogas productivity. From the first day of the charge to the kPa recorded on the 30thday. 6thday, it varied from 0.10 kPato 0.49 kPa, from the 6th to the 18th day, it reached a maximum value of 12 kPa, from the 18th The kinetics of daily biogas production is shown in figure 13. to the 23rdday, there is a slight down to 11.66 kPa and from 23rd

International Journal of Engineering Science and Computing, September 2018 18931 http://ijesc.org/ FIGURE 13 DAILY PRODUCTION CURVE OF BIOGAS 4.50 4.00 3.50

3.00 ) 3 2.50 2.00 1.50 Biogas (m Biogas 1.00 0.50 0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time of digestion (d)

Figure 13 shows that during 30 days of digestion in an with a value of 4m3. After the 16th day, production fell atmosphere of 28.23°C on average, during the first four (4) gradually until the 30th day, for a minimum value of 0.10m3. days of digestion (hydrolysis and acidogenesis phases) of the This kinetics of daily production is consistent with the results biogas production is very weak and unrecorded. The of some authors [2].The kinetics of cumulative biogas maximum production of biogas was recorded on the 16th day production is shown in figure 14.

FIGURE 14 CINETIC OF CUMULATED PRODUCTION 40.00 35.00

30.00 ) 3 25.00 20.00

Biogas (m Biogas 15.00 10.00 5.00 0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time of digestion (d)

Figure 14 shows a low cumulative production of acetogenes is take place. Second phase is called the biogasinitially, then an acceleration of production to decline exponential phase, it corresponds to the central part of the or slow down at the end. The cumulative production of production curve. This phase lasted 16 days, from the 5th to biogasduring the 30 days of digestion is 38 m3. This kineticsis the 21stday, with a high cumulative biogas value of 36.15m3. consistent with the results of several other authors [21]-[22]. It The last phase corresponds to a low production of biogas presents the following three phases: under the effect of the exhaustion of the substrates. It takes First phase:latency phase, the duration of this phase depends place from the 21stdayuntil the end of digestion. on the nature of the substrate. It lasted 5 days, with a verylow Figure 5 shows the biogas produced is rich in methane production of 0.5 m3. This period corresponds to the through the supply of a lamp and the temperature of the liquefaction phase during which hydrolysis, acidogenesis and combustion flame of the biogas which a mounts to 160°C.

FIGURE 15 TESTING THE PRODUCT BIOGAS

a) Combustion flametemperature of biogas b) Lamp lit

International Journal of Engineering Science and Computing, September 2018 18932 http://ijesc.org/ IV. CONCLUSION [11]. FLORENTINO, H.O (2003)„‟Mathematical tool to size In this study we have dimensioned, built and tested a Chinese rural digesters. Scientia Agricola, Piracicaba, Vol 60, Number digester modelhavinga total volume of 2.30 m3with a 1, Pp. 185-190. gasometric part of 0.35m3. The analysis of cow dung samples gives for the dry matter content (21%), the organic matter [12] Cheng, S., Li, Z., Mang, H.P., Huba, E.M., Gao, R. and content (54%), the carbon content (31%), the moisture Wang, X., (2014), “Development and application of content (73%) and pH (7.5). During the 30 days of digestion, prefabricated biogas digesters in developing countries”, the average temperature in the digester is 28.23°C, the Renewable and Sustainable Energy Reviews, Vol 34, Pp 387- pressure of the biogas varies from 0.10 to 12 kPa, the pH of 400.

6.0 to 8.50 and the cumulative production of biogasis 38 m3. The obtained gas wastested by the ignition on a biogas lamp [13] Y. CAMARA, X. CHESNEAU et C. KANTE and the measurement of the combustion flame temperature (2018)„‟Numerical study of thermal comfort in a bioclimatic gives 160°C. At the end of this work, were commend the use habitat in stabilizedearth bricks for a typical climate of of a gas analyzer to determine the chemical composition of Guinea‟‟, Journal Afrique SCIENCE, Vol 14, Number2, Pp the biogas produced. 238-254.

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International Journal of Engineering Science and Computing, September 2018 18933 http://ijesc.org/