What are the considerations for building a domestic biogas well?

Rural household biogas digester design specifications

1, scope

This standard specifies the rural household biogas digester (hereinafter referred to as the biogas digester) design principles require the determination of geometric dimensions and structural design.

This standard applies to brick, cement as building materials, human and animal feces as the main fermentation raw materials for semi-continuous fermentation of domestic small (fermentation room 10m3 or less) water-pressurized biogas digester design.

2, references to standards

The following standards contain provisions, by reference in this standard and constitute the provisions of this standard. At the time of publication of the standard, the version shown are valid. All standards will be revised, the use of this standard parties should explore the possibility of using the latest version of the following standards.

GB/T4750---1984 standard atlas of rural household water pressure type biogas digester

GBJ 3---88 Masonry Structural Design Specification

GBJ9---87 Building Structural Load Specification

GBJ10---89 Concrete Structural Design Specification

3 , design principles

3.1 Biogas digester should be built below the surface of the animal pens or toilets, feeding room connected to the entrance of human and animal manure.

3.2 Adhere to the applicable, sanitary, reasonable layout, beautiful appearance.

3.3 The thickness of the top of the pool cover is not less than 200mm.

3.4 Strength of the coefficient of safety K ≥ 2.65.

3.5 Normal service life of 20 years or more.

4. Design requirements

4.1 Design technical parameters.

4.1.1 Biogas pressure.

4.1.1.2 Maximum working pressure 13KPa.

4.1.2 Gas production rate: 0.15m3/m3, d; 0.2m3/m3, d;

0.25m3/m3, d; 0.3m3/m3, d.

4.1.3 Pitching volume

4.1.3.1 Minimum pitching volume by 50% of the total volume of the fermentation room.

4.1.3.2 The maximum feed is 90% of the total volume of the fermentation chamber.

4.1.4 Gas storage Normal gas storage is 50% of the daily gas production.

4.2 Process flow

Human and animal manure (grass and agricultural waste)→feeding room→anaerobic fermentation room→hydropressure (discharge) room→farmland. In places with conditions, human and livestock manure can be divided into two feed ports into the anaerobic fermentation room.

4.3 Shape and plan layout

Shape and plan layout are selected according to GB/T4750.

4.3.1 The shape of the fermentation room is mainly circular, and the fermentation room can be designed as ellipsoidal or single-span arch rectangle if it is limited by the floor space or the water table is high.

4.3.2 Layout

4.3.2.1 The biogas digester should have a layout design, and the construction design can only be carried out after obtaining the consent of the users.

4.3.2.2 Layout should meet the following requirements:

a) make full use of land resources, compact layout;

b) toilets and corrals are separated;

c) easy to feed and discharge;

d) the gas conduit and the gas pipeline will not be damaged;

e) the angle of the center line between the feed and discharge should be more than 90 °. The squatting plate surface of the feeding room should be higher than the plane of the fermentation room, and the discharging room should be lower than the plane of the fermentation room.

4.3.2.3 A movable cover should be added to the digester which is built with reinforced concrete slab or has the habit of feeding grass.

4.3.2.4 The feed and discharge compartments must be covered, and the cover should be made of components with sufficient strength level. Surface treatment shall be provided around the feeding and discharging compartments.

4.4 Volume of anaerobic fermentation room

4.4.1 Formula for calculating the volume of fermentation room

V=(V1-V2)K1 ----------------------------------------------------- (1)

In the formula: V--- fermentation room Volume m3;

V1---volume of fermentation material m3;

V2---volume of gas chamber m3;

K1---volume protection coefficient, taken as 0.9-1.05.

4.4.1.1 Volume of fermentation material;

V1=[(n1+n2)k2+n3]T ---------- -----------------------------------(2)

The formula: V1 --- fermentation material liquid volume m3; n1 is the total amount of manure produced.

By resident population x 0.006m3/head, d ~ 0.0013m3/head, d take the value of m3;

n2 - is the total amount of livestock manure production.

By the number of pigs × 0.006m3/head, d ~ 0.15m3/head, d take the value of m3;

n3 - the total amount of manure that can be quantitatively collected outside the house per day m3

k2 - the collection coefficient, take the value of 0.5 ~ 1.0;

T- raw material retention period (d); vegetable area t take 30, flat dam agricultural area take 35, hilly agricultural area take 40. -- gas chamber volume m3;

K3 -- raw material gas production rate, according to this specification 4.1.2 to take the value.

4.4.2 The volume of the fermentation chamber is not less than 6.0 m3, (farmers raising more than 10 pigs or more than 3 cows) should use other processes, and when carrying out the construction design, adjustments should be made in the relevant parameters.?

5. Determination of biogas geometry

5.1 Volume and geometry of fermentation room

After calculating the volume according to 4.4.1, then calculate the geometrical dimensions of the pool cover chipping sphere, the pool bottom chipping sphere and the cylindrical pool body according to the following formula.?

The total volume of the fermentation room is calculated according to the following formula: ?

5.1.1 The diameter of the digester is determined according to the user's floor plan.

5.1.2 Net volume and sagittal height of fermentation chamber lid chipping sphere.

5.1.2.1 Calculate the cover chipping sphere vector height according to the following formula.

f1 = D/a1---------------------------------------------------------------(4)

Where: f1 --- pool cover chipping sphere body vector height m;

D-cylinder shape pool body diameter m;

a1-ratio of diameter vector height, take 5-6.

5.1.2.2 Calculate the net volume of the pool cover chipping sphere body according to the following formula

Q1 = π/6f1(3R2-R)--------------------------------------- -------(5)

In the formula: Q1 - cover chipping sphere net volume m3;

π - circumference, take 3.1416;

f1 - cover chipping sphere vector height m;

R -internal radius of the pool body cylinder m.

5.1.3 Volume of the pool body cylinder and height of the pool wall in the fermentation room

5.1.3.1 Net volume of the pool body cylinder in the fermentation room

Q2=V-Q1-Q3 ------------------------------------- -------------------(6)

In the formula: Q2-fermentation room pool body cylinder net volume m3;

V-fermentation room total volume m3;

Q1-pool cover chipping sphere net volume m3;

Q3 - net volume of chipping spheres at the bottom of the pool in the fermentation room m3.

5.1.3.2 Cylindrical homogeneity of the body of the pool in the fermentation room

H=Q2/πR2-----------------------------------------------------------(7 )

Where: π-circumference, taking the value of 3.1416;

R-radius of the cylinder of the body of the fermentation room pool m;

H-height of the cylinder of the body of the fermentation room pool m.

5.1.4 Sphere sagittal height of clipping sphere at the bottom of the fermentation room pool and net volume .

5.1.4.1 Calculate the pool bottom chipping sphere vector height according to the following equation.

f2 = D/α2---------------------------------------------------------------(8)

Where: f2 - pool bottom chipping sphere vector height m;

D -diameter of the pool body cylinder m;

α2-ratio of the diameter to the bottom of the pool body vector height, take the value of 8-10.

5.1.5 Calculate the net volume of the pool body chipping sphere according to the following formula.

Q3=π/6f2(3R2-f22)--------------------------------------------------------------(9)

Formula: Q3-fermentation inter-pool bottom chipping sphere net volume m3;

π-circumference, take 3.1416;

f2-sagittal height of the chipping sphere at the bottom of the pool m;

R-radius of the inside of the cylinder of the pool body m.

5.2 Surface area

The total surface area in the fermentation room is calculated according to the following formula?

S=S1+S2+S3-----------------------------------------------------------------(10)

In the formula: S-total surface area inside m2;

S1 -internal surface area of pool cover chipping sphere m2;

S2 -internal surface area of pool body cylinder m2;

S3 -internal surface area of pool bottom chipping sphere m2.

5.2.1 Calculation of the internal surface area of the spherical surface of the pool cover chipping sphere.

5.2.1.1 Calculate the radius of curvature of the pool cover chipping sphere surface according to the following formula:

ρ1=D2+4f12/8f1=R2+f1/2f1--------------------------------------------------(11)

In the formula: ρ1 - radius of curvature of the pool cover chipping surface m;

R-radius of the pool body cylinder m;

D-inner diameter of the pool body cylinder m;

f1-pool painting chipping sphere inner surface sagittal height m.

5.2 .1.2 Calculate the inner surface area of the pool cover chipping sphere according to the following formula

S1=2πρ1f1=π(R2+R) ----------------------------------------------------(12)

In the formula: S1-Interface of the pool cover chipping sphere Surface area m2;

R-R-radius of the pool body cylinder m;

ρ1-radius of curvature of the pool cover spherical surface m;

f1-vectorial height of the pool cover spherical surface m;

π-radius of the circumference, taken as 3.1416.

5.2.2 Cylindrical pool body internal surface area

S2 = πDH ------------------------------------------------------------(13)

Equation: S2- Internal surface area of the pool body cylinder m2;

D- diameter of the pool body cylinder m;

H- height of the pool body cylinder m;

π- circumference, take 3.1416.

5.2.3 Internal surface area of the pool bottom chipping sphere

5.2.3.1 Calculate the radius of curvature of the chipping sphere at the bottom of the pool according to the following formula?

ρ2=D2+4f1α2/8f2=R2+f22/2f2------------------------------(14)

In the formula: ρ2-radius of curvature of the pool bottom chipping sphere body m;

D-inner diameter of the pool body cylinder m;

5.2.3.3.3 Calculate the inner surface area of the pool bottom chipping sphere body as follows Diameter m;

R-radius of the inner radius of the pool body cylinder m;

f2-height of the inner sagittal of the pool chipping sphere m.

5.2.3.2 Calculation of the inner surface area of the pool chipping sphere by the following formula

S3=2πρ2f2=π(R2+f22)--------- ------------------------------(15)

In the formula: S3-Internal surface area of Ikedu chipping sphere m2;

ρ2-Radius of curvature of Ikedu chipping sphere m;

f2-Ikedu chipping sphere sagittal height m;

R-internal radius of the cylinder of the pool body m;

π-circumference, take 3.1416.

5.3 Feeding compartment

5.3.1 Feeding compartment consists of squatting plate, feed inlet (tube).

5.3.1.1 Squatting plate geometry. Squatting plates are divided into ordinary squatting plates and maggot-proof squatting plates.

a) ordinary squatting board geometry is: length × width × thickness = 720mm × 420mm × 80mm, the central reserved length × width = 360mm × 1 50mm and rectangular holes;

b) maggot-proof squatting board geometry: maggot-proof squatting board planes and the central square holes of the same dimensions, in order to achieve the effect of maggot-proofing should be added to the middle of the central square holes of 120mm in height. Width of 40mm maggot-proof line. Conditions should be in the surface paste glossy tiles or glass.

5.3.1 The feed opening (tube) consists of an upper rectangular slot and a lower garden tube.

a) The geometry of the upper middle rectangular trough is L×W×D = 600mm×320mm×500mm;

b) The lower middle garden pipe should be Φ200-Φ300 precast concrete pipe or cast-in-place concrete pipe, and the angle between the pipe and the wall of the pool should not be less than 30°

5.3.2 Farmers who have the conditions should add a human feces treatment device before the feeding, whose volume is Calculated according to the following formula:

Q4 = n1 × m × 30 ÷ 1000 -----------------------------------------------------------(16)

In the formula: Q4 - human waste treatment pit volume m3;

n1-per capita daily production of feces kg;

m-number of people entering the toilet, people;

30-feces treatment time, days.

5.4 Discharge room (water pressure room)

5.4.1 Discharge room has three roles:

a) slag discharge;

b) into the pool for maintenance;

c) regulating the pressure in the pool;

d) controlling the minimum feeding amount.

5.4.2 The design of the discharge compartment shall comply with the following requirements:

a) Above the level of the maximum feeding volume is the water pressure compartment, and the section of the water pressure compartment (horizontal section) can be round, oval

or long main shape;?

b) The geometry of the doorway connecting the fermentation compartment to the discharge compartment is: height calculated in accordance with 4.1.3 Minimum pitching volume, and width 500mm

～700mm.

5.5 The geometric dimensions of the fermentation compartment and the discharge compartment may be selected in accordance with the attached table.

6. Structural design of biogas digester

6.1 General provisions for structural design

6.1.1 Brick and cast-in-place concrete, stone and cast-in-place concrete, precast reinforced concrete blocks and cast-in-place concrete combination structure, or all-concrete structure can be used. According to GBJ3 regulations monthly average gas mix is lower than -50C areas, the exposed part of the digester, shall not use block structure.?

6.1.2 When using this specification, for the determination of general loads, calculation of component sections and foundation design, etc., should be implemented according to the provisions of the corresponding

national standards or codes. For the construction of biogas digester structure

design in seismic areas, wet trap loess or expansive soils, etc., should also be in line with the current provisions of the relevant standards and codes.?

6.2 Load

6.2.1 Biogas digester design load, according to the principle of GBJ9, according to its nature can be divided into the following two categories:

a) Constant load: including structural weight, soil pressure (soil vertical and lateral pressure), etc.;

b) Live load: including water pressure (liquid pressure of the pool liquid, groundwater pressure, buoyancy, design water pressure). Pressure and other facilities (corrals, troughs, etc.) loads and people, animal loads, etc.

6.

6.2.2 Loads acting on the ministries

6.2.2.1 Loads acting on the pool cover

a) Self-weight load: self-weight load according to the material of the pool cover, in general, the weight of the brick body to take 19kN/m3, cement mortar 20KN/m3, concrete 23 ~ 24KN/m3;

b) overburden load: Because the pool cover is clipped spherical, so the overburden load is a variable, it is reduced with the reduction of the half-tension angle and the corresponding reduction , the design, the filler capacity is generally taken as 18KN/m3

c)Live load: the standard value of the uniform load on the ground is generally taken as 2KN/m2;

d)Barometric load: it is generally taken as 12kp.

6.2.2.2 Acting on the wall of the pool Load:

a) earth pressure caused by the ground live load;

b) earth pressure above the water table;

c) earth pressure below the water table;

d) hydrostatic pressure generated by the groundwater;

e) hydraulic load of fermentation material liquid in the pool;

f) pneumatic pressure load in the pool.

6.2.2.3 Loads acting on the bottom of the pool:

a) pool air pressure loads perpendicular to the inner wall of the pool bottom;

b) hydraulic loads of the fermentation material in the pool;

c) all vertical loads that can be transmitted from above the boundary of the bottom of the pool;

d) self-weight loads of the bottom of the pool;

e) reaction force of the foundation soil on the bottom of the pool ;

f) groundwater uplift force.

6.3 Load combinations,

The most unfavorable load combinations shall be calculated in the design.?

6.3.1 Load combinations for pool cover

6.3.1.1 The most unfavorable combination of radial force for pool cover is: self-weight of pool cover + overburden load + ground live load.

6.3.1.2 The most unfavorable combination of circumferential forces on the cover is: cover weight + soil overburden load + air pressure load.

6.3.2 Combination of cover bearing loads

The most unfavorable combination of cover bearing loads is the horizontal thrust generated by the combination of cover weight, overburden load, and ground live loads.

6.3.3 Pool wall load combinations.

6.3.3.1 Construction stage: Strength is not up to the design mark, should be calculated according to the actual mark, its load in addition to self-weight, should also be considered in addition to the wall backfill soil tamping pre-pressure.?

6.3.3.2 Use of the stage:

a) for the ring tension, no groundwater action, no ground live load action when the casting of gas production stage is the most unfavorable;

b) for the bending moment, the empty pool situation in the joint action of groundwater, ground load, earth pressure is the most unfavorable case.

6.3.4 Pool bottom load combination

Empty pool is the most unfavorable case, when the loads are the pool bottom foundation reaction force and the line load of the body of the pool uniformly distributed along the circumference of the pool.?

When the strength of the foundation at the bottom of the pool is checked, the feeding stage of gas production is the most unfavorable situation; when the biogas digester is checked for flotation resistance, the empty pool is the most unfavorable situation.?

6.4 Constructional requirements

6.4.1 The blocks and mortar used to construct the digester, according to the provisions of GBJ3-8821?1, shall comply with the following strength level requirements: ?

a) Strength grade of sintered ordinary bricks: MU10~MU15

b) Strength grade of concrete blocks: MU15~MU20

c) Strength grade of stone: MU30~MU40

d) Strength grade of mortar: masonry mortar>M7.5, plastering mortar>1:3.

6.4. 2 Concrete used for construction of biogas digester, sweep GBJ10-892 1.1, shall meet the following strength requirements:

a)Strength grade of cast-in-place concrete is not less than C15;

b)Strength grade of prefabricated reinforced concrete is not less than C20.

According to GBJ10 -89 Article 7.1.1, when the thickness of precast reinforced concrete slab is less than 150mm, the spacing of reinforcement is not

less than 200mm, and the diameter of reinforcement is not less than 6.5mm.

6.4.3 Requirements for the section of each part:

a)The thickness of concrete for spherical pool cover is not less than 60mm;

b)Thickness of pool wall: block for curved wall is not less than 60mm; cast-in-place concrete is not less than 60mm, square pool wall: block masonry thickness is not less than 120mm, cast-in-place concrete thickness is not less than 100mm;

c)Thickness of concrete of the bottom plate of the chipping pool is not less than 60mm.

6.5 When sealing anticorrosive coating is used in the methane digester, the coating should Meet the following requirements:

a)Water-based coating with good wet-setting properties and strong water-absorbing capacity;

b)Air permeability coefficient should be less than 1010cm3, cm/cm2, s, dapa;

c)Good affinity with cement mortar.

Precautions for safe operation of biogas digester

In order to ensure normal gas production, safe operation of biogas digester and eliminate unsafe accidents, the following aspects should be paid attention to in the daily management and operation.

I. When excavating, safety measures should be taken to protect the safety of construction workers.

Two, maintenance, must be sealed with a temporary cover for each exposed mouth, to prevent people and animals step on the air, fall into the pool.

Three, after feeding, must seal each outlet. When the start of gas production, the exhaust gas should be discharged for more than 30 minutes a day to prevent the air pressure is too high to lift the movable cover.

Four, it is strictly prohibited to test the fire in the mouth of the gas conduit, in order to prevent the occurrence of backfire, causing the pool explosion and other unsafe accidents.

Fifth, the use of light cooker should be carefully read before the use of instructions, specific use should be standardized operation, timely clean up the surface of the stove debris.

Sixth, when the biogas pressure reaches nine air pressure, should be timely deflation, so as to avoid high air pressure damage to the pool.

Seven, it is strictly prohibited to build a fire within 5 meters of the biogas digester to prevent unsafe accidents.

VIII, often check the activities of the cover is sealed intact, prohibited in the activities of the cover to step on.

nine, often check the gas pipeline connections whether the leakage, if there is a rotten egg smell indoors, you should immediately turn off the gas source, open the windows and doors to ventilate, evacuate people. Strictly prohibit the ignition, to be relatively odorless indoor, as soon as possible to repair the leakage parts.

Ten, clear the pool or check the pool body, should first empty the pool of raw materials, and then use the blower to clear the pool of residual gas, and so on when the oxygen is sufficient, and then under the pool operation, while the operation of the fire is strictly prohibited, if you need to illuminate the use of flashlights or electric lamps.

Eleven, biogas digester is not a garbage pit, it is strictly prohibited to put all kinds of pesticides and heavy metal compounds, salts and other organic wastes into the pool, so as to avoid poisoning of biogas digester.

Twelve, the use of methane fertilizer, should be strictly in accordance with the required concentration of application, in order to avoid fertilizer damage.