Design and Construction of Rural Household Hydraulic Biogas

AGENDA § 1. Brief introduction § 2. The development of biogas digester in China § 3. Structure of hydraulic biogas digester § 4. Advantages of hydraulic biogas digester § 5. Three key points for design of hydraulic biogas digester § 6. Design § 7. Summary of design parameters § 8. Construction Copyright © 2012 APEC Secretariat

1. Brief introduction China is one of the countries that use biogas early in the world. In 1920, Mr. Luo Guorui built a biogas digester called “Chinese Guorui Natural Gas Store”, which was the first Hydraulic Digester in China. Copyright © 2012 APEC Secretariat

Guorui Natural Gas Store Copyright © 2012 APEC Secretariat

2. The development of biogas digester in China rural areas Since 1980 s, biogas

2. 1 The number of biogas digester in China rural areas By the end of 2009, there about 35 million household biogas digesters have been built and annual biogas production is 10. 2 billion m 3 in China rural areas. There about 4. 5 million household biogas digesters in operation in Sichuan Province. Copyright © 2012 APEC Secretariat

Development trend chart of rural household digester (104) Copyright © 2012 APEC Secretariat

2. 2 Distribution of household biogas digester application in China Rural household digesters are distributed in 31 provinces all over the country. Over 16 provinces constructed 200, 000 digesters each. Sichuan Province has the biggest amount of digesters as much as 4. 5 million. Copyright © 2012 APEC Secretariat

2. 3 Programs and plans By the end of 2010, there will be 40 million households with biogas digesters and the annual biogas output shall reach 15. 5 billion m 3 and the dissemination rate shall reach 30%; 4000 large biogas plants shall be built on husbandry farms and 336 million m 3 biogas shall be increasingly produced. Copyright © 2012 APEC Secretariat

2. 3 Programs and plans By the end of 2020, there will be 80 million households with biogas digesters and the dissemination rate shall reach 70%; 8000 large biogas plants shall be built on husbandry farms and 44 billion m 3 biogas shall be produced. Copyright © 2012 APEC Secretariat

2. 4 Standards By the end of June 2008, 89 rural energy standards have been formulated or revised and 69 of them are in operation; Among all the issued standards, 18 standards cover rural biogas. Copyright © 2012 APEC Secretariat

2. 4 Standards Rural household biogas: 18 standards including 6 national standards and 12 industrial standards, covering biogas digester drawings, rules for construction, check and acceptance, biogas cookers and related products, integrated utilization of biogas technologies. Copyright © 2012 APEC Secretariat

3. Structure of hydraulic biogas digester 3. 1 What is a biogas digester ? A sealing digester that can produce biogas through anaerobic digestion by various microbes is a biogas digester. Copyright © 2012 APEC Secretariat

3. 2 Structure of hydraulic biogas digester 1—Inlet; 2—Inlet pipe; 3—Fermentation chamber; 4—Gas chamber; 5—Movable plug; 6—Biogas guide; 7—Outlet pipe; 8—Hydraulic chamber ; 9—Overflow pipe. 10—Storage tank. Copyright © 2012 APEC Secretariat

1—Inlet: It’s laid of brick. The function of inlet is to feed raw material.

2—Inlet pipe: The inlet pipe is made of concrete, inserting aslant into lower part of digester. It is easy to build, feed and agitate. Diameter of the inlet pipe is usually 20 -30 cm. Copyright © 2012 APEC Secretariat

3—Fermentation chamber: Fermentation chamber is the main part of a biogas digester. Raw material is mixed according to the process technology and fed into it. It should be leak -proof for water. Copyright © 2012 APEC Secretariat

4—Gas chamber: Gas chamber must be leak-proof for biogas. The function of gas chamber

5—Movable plug: The movable plug is at the top center of the biogas space. It can be open or close as required. Usually we fill some stick clay around the edge of the plug to seal it and store some water above the plug. In order for a person getting in or out, diameter of movable plug is usually 60 cm. Movable plug is useful when user wants to ventilate the chamber or feed raw material during starting up or discharge when needed. When the pressure is high inside, the movable plug can be burst open to protect the biogas digester. Copyright © 2012 APEC Secretariat

6—Biogas guide: The gas guide is made of copper, the diameter is usually 810

7—Outlet pipe: Outlet pipe is round shaped. It is installed aslant at middle or

8—Hydraulic chamber : It’s laid of brick, the function of hydraulic chamber is to

9—Overflow pipe: The overflow pipe is located at the center between hydraulic chamber and storage tank, the diameter is 10 -15 cm. The overflow pipe must be 20 cm underground at least. Copyright © 2012 APEC Secretariat

10—Storage tank: The storage tank is a tank which can store the digested effluent

3. 3 Principle of hydraulic biogas digester When a biogas digester produce biogas, the

3. 3 Principle of hydraulic biogas digester On the contrary, when biogas is used, liquid get back into the digester from the hydraulic chamber so the liquid level drops. In this way, internal and external pressure is balanced. That’s why we call it hydraulic biogas digester. Copyright © 2012 APEC Secretariat

4. Advantages of hydraulic biogas digester 1. Good performance, good adaptability for construction material; 2. Simple structure, easy for construction; 3. Low cost; 4. Convenience for use and operation; 5. Long service life: about 20 -25 years. Copyright © 2012 APEC Secretariat

5. Three key points for design of hydraulic biogas digester 1. Circle—The shape of digester should be circle, the raw material can be mixed completely. save building material; intensity of the structure is even, good for service life. 2. Small— The volume of digester should be small , usually less than 10 cubic meters; there are four kind of volumes: 4, 6, 8, 10 cubic meters; it’s enough for cooking three meals according to different family members. 3. Shallow—The depth of digester should be shallow, usually less than 2. 5 meters. It will be easy for construction (avoid ground water) and convenient for discharge also. Copyright © 2012 APEC Secretariat

Schematic diagram of digester size • • H 0 =D 0/2. 5 f 1

6. Calculation (1) • From volume formulas of ball cap and cylinder, • we

Put f 1, f 2, D 0 and H 0 into the above formulas,

6. Calculation (2) • Total volume of the digester is: • V=V 1+ V

6. Calculation (2) • If we have determined the volume of a biogas digester

Example 1: • Assuming a biogas digester with volume of 10 m 3 is to be built, its diameter is: • D 0=1. 3078× 2. 155 =2. 818(m) • Volume of each part is: • V 1= 0. 0827× 2. 8183=1. 85 m 3 • V 2= 0. 0501× 2. 8183=1. 12 m 3 • V 3= 0. 3142× 2. 8183=7. 03 m 3 Copyright © 2012 APEC Secretariat

Example 1: Other geometric parameters: • From the above, we get: • f 1

6. Calculation (3) Calculation for surface area: • F=F 1+ F 2+ F 3

Exercise 1: • Assuming a biogas digester with volume of 8 m 3 is to be built, its geometric parameters are: • D 0=? H 0 =? f 1 =? f 2 =? R 0 =? • ρ1=? • • ρ2=? Volume of each part is: V 1= ? m 3 V 2=? m 3 V 3= ? m 3 Copyright © 2012 APEC Secretariat

Table for dimension of digester Copyright © 2012 APEC Secretariat

6. Calculation (4) Calculation for volume of hydraulic chamber (outlet chamber) : Volume of hydraulic chamber equals to gas production for a half day, i. e. : • Vh=V×rv× • Where, • Vh= Volume of hydraulic chamber (m 3) • V = Volume of biogas digester (m 3) • rv = Gas production rate (m 3/d) Copyright © 2012 APEC Secretariat

Example 2: Calculation for volume of hydraulic chamber If : V = 8 m 3, rv = 0. 35 m 3/d, then Vh= 8× 0. 35× = 1. 40 m 3 Namely, volume of hydraulic chamber is 1. 40 m 3. Copyright © 2012 APEC Secretariat

6. Calculation (5) Determination of digester volume : If we have known gas production rate, raw material quantity, biogas consumption person per day and number of family members, we can calculate the volume of biogas digester by the following formula: Average biogas consumption person×number of persons V= Gas production rate Copyright © 2012 APEC Secretariat

Example 3: Calculation for volume of hydraulic chamber • Assuming biogas consumption is 0. 3 m 3/per person per day, number of family members is 5 and gas production rate is 0. 25 m 3/d. Then : V= = 6 (m 3) Copyright © 2012 APEC Secretariat

7. Summary of design parameters 1. Maximum working pressure in digester is 7840 Pa

3. Volume of hydraulic chamber is half biogas production per day; 4. Thickness of

5. Live load above the digester should be 2 kpa (200 kg/m 2); 6. Groundwater level should be lower than one meter depth from the ground; 7. Load bearing capacity of foundation requires more than 50 kpa (5 t/m 2). Copyright © 2012 APEC Secretariat

8. Building materials 1. Clay brick—the most popular material for building digester in China countryside; the geometric dimension is 240 x 115 x 53 mm. 2. Stone blocks—be adopted in mountain areas. 3. FRP—Fiber Reinforced Plastic (Fiber Glass). 4. Concrete—it’s consists of cement , sand, gravel and water. There are 4 intensity grades, that is: C 10, C 15, C 20, C 25. C 10 and C 20 are used for building digester. 5. Plaster(cement mortar)-- it’s consists of cement , sand, and water. The ratio of plaster for laying is 1: 3. Copyright © 2012 APEC Secretariat

9. The composition ratio of concrete (1 m 3 concrete) Intensity grade Cement (kg) Sand (m 3) Gravel (m 3) Water (kg) C 10 200 0. 43 0. 92 172 C 15 250 0. 92 172 C 20 315 0. 50 0. 90 182 C 25 350 0. 45 0. 85 182 Copyright © 2012 APEC Secretariat

10. The estimated quantity of building material Volume (m 3 ) Brick (piece) 4 6 8 10 800 1000 1300 1500 Cement (ton ) 0. 8 1. 0 1. 2 1. 3 Sand (m 3 ) Gravel (m 3 ) 1. 2 1. 4 1. 5 1. 7 0. 8 1. 0 1. 2 1. 5 Working days (day) 12 15 17 20 Copyright © 2012 APEC Secretariat

11. The prices of local building material and workers’salary Material Price (CNY) Brick (1000 pieces) 400 Cement (ton ) 450 Sand (m 3 ) 90 Gravel (m 3 ) 60 Workers Technician Labour Salary (CNY/d) 80 -90 60 -80 Copyright © 2012 APEC Secretariat

12. Construction 12. 1 Lay out and digging: Before digging, the digester should be lay out first depending on the digester size and soil quality. For digester construction, firstly a pit should be dug. It is shaped like the larger part of a cone. Copyright © 2012 APEC Secretariat

Table 1. Maximum slope for different soil Copyright © 2012 APEC Secretariat

12. 2 The central rod and radius gauges It is important to set a rod at the center for the cylinder digester construction to keep digester wall circular and vertical regularly. Link the two couples of diagonal stakes at four corners. Hanging a tag at the point of intersection to determine the center of the digester. Stand a rod at the center, and then fasten the upper part of the rod with threads as shown in Figure a. The central rod should not be moved after it positioned during construction. Copyright © 2012 APEC Secretariat

12. 3 The central rod and radius gauges The circular shape of the digester is controlled by the radius gauges. Use them to check every block of the digester wall. After complete one layer of laying work, move the radius gauges up with a height as the thickness of a layer. The gauges must be always kept horizontally. Copyright © 2012 APEC Secretariat

12. 4 Construction of the digester dome In order to ensure geometric size of the dome, usually we use inflexible wire as radius gauge for laying dome bricks. If the center of the dome curvature is lower than the digester bottom, a small pit is dug in advance as shown in Figure d. The pit can be filled after the dome is completed. Copyright © 2012 APEC Secretariat

12. 5 Safety during construction Collapse prevention: During digging the digester, the wall should be of proper slope depending on the soil quality. Some measurements must be taken to fix the poor quality soil. Heavy article is not allowed to put near digester side. Water must be drained during rainy season. Copyright © 2012 APEC Secretariat

12. 5 Safety during construction During dome construction without mould, use flat stones to insert into gaps between bricks tightly. No people are allowed to stand on the dome until the soil become hardened. Heavy articles are not allowed to put on newly built dome to avoid collapse due to over load. Copyright © 2012 APEC Secretariat