Renewable Energy Technology 3(2+1)

Lesson 13. Periodical maintenance of biogas plants

(i) Daily routines, (ii) Weekly routines, (iii) Monthly routines and (iv) Half Yearly/Yearly routines.

Daily Routines/Maintenance

1. About 25 kg of cattle dung is required for generation of 1 m³ gas per day (calculated at 1.4 cft/kg).  For higher capacities, the dung required for daily feeding is (25 x X) kg, where X is the capacity of the plant. The required quantity of dung along with equal quantity of water is fed into the mixing tank after plugging the inlet pipe.  The contents are thoroughly mixed.  Materials like, straw, trash etc. should be removed.  The slurry is then led into the digester by removing the plug put at the opening of the inlet.

After feeding, the inlet opening is again closed by the plug.  The inlet tank is cleaned with water and the washing is drained out through the hole provided at the lowest point of the floor of the inlet tank.  Inorganic materials like sand, mud, etc. will get washed away while cleaning the mixing tank.

2. In the case of KVIC model, the gas holder is given half rotation in clockwise and anticlockwise direction 2-3 times, immediately after feeding to break the scum on the surface of the digester slurry.  This is to be repeated once more during the day, when the gas holder has submerged in the slurry.

3. As far as possible, the main gate valve is opened only when gas is required.  In any case, it should be made as a practice to close the gate valve at night, when no more gas is required.  Next day the valve is opened when use of gas is to start.

4. The air shutter’s position is checked while starting the use of burner in the morning and is properly readjusted, if necessary.

5. In the case of KVIC model, during the first month after commissioning the plant, it is likely that the outlet pipe is chocked by hard cattle dung that must have gone into the digester at the time of initial feeding.  It may therefore be checked about the flow of the slurry from outlet pipe immediately after daily feeding.  If there is any chocking, it may be cleared by inserting a long bamboo into the outlet pipe.

6. In winter, the rate of gas production would be low.  As such it is better to use a little warm water for daily feeding so that slurry with lower temperature may not disturb the system inside the digester when daily feeding is done.  One way is to make the slurry in the mixing tank in the morning and allow to get warm by direct solar energy.  This slurry may be allowed inside the digester when no more sun rays fall on the slurry.

Weekly routines/Maintenance

1. The burners and lamps are to be cleaned.  Particularly dirt, dust etc. if any at the ports and injector orifice of the burners are removed.  Smooth gas flow must be ensured; Similarly the nozzle of biogas lamp and the chimney are also cleaned.

2. The water remover/water trap may be checked for any collection of water and the condensed water any be drained out, the plug is properly fitted again. If it is an automatic water remover, it may be checked for its proper functioning.

3. In the case of fixed dome plants, a long bamboo may be inserted in the digester through the outlet gate and stirring is done to prevent accumulation of scum.

4. In the case of KVIC model, the dry mat that must have been collected in the gap between the digester wall and the gas holder may be removed manually, so that smooth vertical motion of the gas holder is not disturbed.

Monthly Routine/Maintenance

1. Gate valve and gas pipe line be tested for leakage and rectification is  done if found necessary.

2. Gas taps/gas cock may need lubrication which may be done.

3. Ventury and mantles of gas lamps may be checked and replaced if necessary.

4. If the manure pit by the side of the gas plant is full, the outlet slurry may be diverted to the next pit.

Half Yearly / yearly Routines/Maintenance

1. Gas holder, dome and pipe line are checked for leakage and corrective steps are taken where necessary. Particularly the flexible pipe connected the gas outlet and the main pipe line (KVIC biogas plant) may be checked for leakage and replaced if found brittle.

2. In the case of KVIC model, outer surface of the mild steel gas holder is prone to corrosion more than the inner surface. For protecting the gas holder from corrosion, outer surface need to be painted once in a year. Some times, it may be necessary to paint in about 6 months, if the earlier painting has not been proper and the atmosphere is humid. It is not necessary to take out the gas holder from its position. When the gas holder if full with gas, the main gate valve may be closed, entire outer surface visible above slurry level is thoroughly cleaned with water. Wire brush may be used for cleaning the rusted portion if any. Black enamel paint is applied over the entire surface. The paint may be allowed to dry for one day and then the gas should be allowed to pass in the pipe line for routine use.

3. Worn out accessories are to be repaired or replaced.

4. The manure from the pits which are full is removed for manuring  purpose and the pits are kept ready for further use.

Do's and Dont's for maintenance of biogas plants

a. Do's:

1. Decide the size (capacity) of biogas plant matching the availability of feed material and requirement of gas for various needs.

2. Select the site for biogas plant which is nearer to the points of use (say kitchen) and also nearer to the cattle- shed, as far as possible.

3. Install biogas plant in an open space where Sun rays are freely falling during day time.

4. Install biogas plant strictly as per the approved drawings and specifications with trained persons.

5. Install the biogas plant below ground level as shown in the drawings (except a small projection in case of KVIC model).

6. Do back filling by filling up the gap between the outer surface of the digester and the portion of the earth cutting, firmly compacting with sand/soil and also putting some water as per installation guidelines.

7. Initial feeding to biogas plant should be done after curing as prescribed.

8. Feed biogas plant with cattle dung and water in 1:1  proportion,  making it a homogeneous mixture after thorough mixing.

9. Remove, straw pieces of sticks, etc. from the slurry (mixture of dung and water) before feeding.

10. Maintain proper slope in the pipeline and fix water remover (water tap) at the lowest point.

11. Break the scum formed on the surface of the slurry in the digester by rotating the gas holder daily after feeding in case of KVIC model and by inserting a long bamboo throughout and stirring the slurry.

12. Use ISI marked burners and lamps to get maximum efficiency.

13. Close the main gas cock in the night after the use of gas is over.

14. Test the burning of the gas at the burner.

15. Use soap solution for testing leakage of gas in the dome/gas holder.

16. Put the burners on a raised platform in the kitchen.

17. Adjust the air shutter to get blue flame to get maximum heat.

18. Use lighter or light the match before opening the gas tap.

19. Cover the inlet and outlet tank openings of fixed dome models with wooden plank, stone or reinforced cement concrete slab.

20. Keep the kitchen ventilated.

21. Paint the outer surface of the gas holder of KVIC model generally once in a year or when rusting is noticed.

b. Don’ts

1. Don't recommend much higher capacity simply because there is enough dung, when the use of gas is less. Don’t suggest a smaller plant because there is less feed material when gas required is much higher.

2. Don't select a site far-away from cattle shed and also kitchen to avoid operational inconveniences.

3. Don't install biogas plant under a tree or under any other shade.

4. Don't introduce any change in the design and/or specification of biogas plant at field level suggestions if any regarding modifications should be referred to MNRE.

5. Don't install biogas plant above ground level.

6. Don't do back filling loosely (or after completion of digester construction in case of KVIC model.

7. Don't start initial feeding without proper curing.

8. Don't add either more water or less water to make a homogeneous mixture with cattle dung for feeding.

9. Don't allow soil or sand particles to entire the digester along with the slurry.

10. Don't lay the pipeline in such a way that condensed water gets accumulated in any portion of the pipeline which disturbs the smooth flow of gas.

11. Don't allow accumulation of scum of the surface of the slurry in the digester.

12. Don't use burners and lamps which are not approved by ISI since they may not give maximum efficiency.

13. Don't leave the gas taps near the burner open after use.

14. Don't test burning of gas at the main gate valve on the dome/gas holder.

15. Don't use fire for testing the leakage in the gas holder.

16. Don't put burners on the ground in the kitchen as in the case of conventional Chula.

17. Don't make the air shutter tight or too loose. In both the cases, there would be incomplete combustion and thus wastage of gas.

18. Don't open gas tap and start searching for lighter and match box.

19. Don't keep the outlet tank open since cattle, children may accidentally fall.

20. Don't inhale biogas since it may be hazardous.

21. Don't allow the gas holder to rust which brings down its life.

(Source : TNAU-Bioenergy-BDTC manual