Maintenance of a Biogas Plant
General
As a general rule, maintenance of agitation, pumping and flushing equipment should always be performed above ground level [5-6]. If this is not possible, a forced ventilation system must be permanently installed in order to counteract the risk of asphyxiation and poisoning in the event of an escape of gas.
Consider these basic operation and maintenance principle:
- To strive and perform optimal, “life support systems” must work at all times, and “living conditions” shall be kept stable and in harmony with process requirements[1]
- Proper biogas O&M is all about stability and harmony, well in line with old Chinese Confucianism principles.[1]
- General good practise O&M procedures can be defined, but also a “feeling” for the individual plants requirements is needed by the O&M staff. [1]
Design interaction
- Suitable and sturdy equipment
- Automatic protection and safety instrumentation to avoid serious break downs
- Redundant installation on key functions, or quickly replaceable complete components on stock
- Operation quickly restored
- Proper service off-line
- Shut off possibilities and easy access where relevant
- Drain and flushing connections where service is foreseen
- Process indication instruments and logging to be able to follow equipment state and trends, in order to react in time
Spare part management
- Keep strategic spare parts and wear parts on stock!
- Strategical spare parts can be foreseen to be needed to keep vital functions running and/or parts with long delivery time
- Wear parts are parts which can be foreseen to wear out periodically, to be able to schedule service without need to wait for parts
- Update relevant spare and wear parts to have on stock according to experience
- Remember to replenish stock as soon as spare parts are used
- Consider to refurbish replaced equipment to keep as emergency spare units
Storage of spare parts
- Keep storage facility dry, clean and ventilated.
- Keep spare parts organized so you know where to find the parts for different equipment.
- Keep parts according to manufacturers recommendation
- Upon receiving of parts: Check that it is the right parts and quantity. Put them in place.
- Spare parts are normally preserved for shipment and storage when delivered, so keep in original packing
Comminutors
According to information supplied by the manufacturers, the equipment is of low-maintenance design. It should be possible to carry out maintenance during the breaks in feeding.[2]
External comminutors
Maintenance can be arranged by contract with the manufacturer and is a necessity, depending on the substrates
worked. A supply of comminuted material to bridge downtimes for maintenance can be stocked on site.
In-pipe comminution agitators
Freestanding units can be serviced quickly without long outages.
Easily accessible apertures significantly speed up cleaning.
| Characteristic values |
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| Suitability |
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| Advantages & Disadvantages |
+ Easy accessibility to the equipment in the event of a breakdown |
| Designs |
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Comminutors combined with conveyor technology in single units
Freestanding pumps can be serviced quickly without long outages; submersible pumps are easily removed from the substrate for servicing. Maintenance apertures make for much shorter downtimes.According to information supplied by the manufacturers, the equipment is of low-maintenance design. Maintenance contracts are available.
It should be possible to carry out maintenance during the breaks in feeding
Hygienisation tanks
The tank must have at least one manhole. Comply with applicable health and safety regulations for working inside enclosed spaces
(due consideration also has to be given to gas safety regulations) The equipment as such (temperature sensors, agitators, pumps) has to be serviced; the tank itself should be maintenance-free.
Pre-digester pit
Depending on the type of agitator, maintenance can be undertaken outside the pre-digester pit or the digester, without process interruption.
If the design lacks provision for removing settlement layer material, this material has to be removed manually. Apart from this, virtually no maintenance outlay; maintenance of the various technical items of equipment is described in the corresponding sections.
Infeed of the substrate
Pumps
Rotary pumps
More difficult in the case of submersible pumps, although relatively easy access through removal apertures. Comply with applicable health and safety regulations for working inside the digester. Outages tend to be slightly longer than for other types of pump.
Eccentric single-rotor screw pumps
Very durable!
The design is inherently service-friendly; outages are short on account of the quick-change design of the screw drive.
Hopper pumps for solids infeed into piped liquid
The design is inherently service-friendly; outages are short.
Rotary displacement pumps
The design is inherently service-friendly; outages are short.
Infeed screw conveyors
Moving parts, so outlay for regular servicing must be taken duly into account. Manual intervention required to clear clogging or remove trapped interfering substances. Servicing of the screw that feeds to the digester necessitates what can be considerable downtime.
Infeed with ram feeder
Moving parts, so outlay for regular servicing must be taken duly into account. Servicing of the ram feeder necessitates what can be considerable downtime, possibly also associated with emptying of the digester.
Digester
Stirred-tank biogas reactors
Manhole facilitates accessibility.
Biogas reactor with plug-flow
- At least one manhole is necessary so that the interior of the reactor can be accessed in the event of a breakdown.
- Comply with applicable health and safety regulations for working inside the digester
Integrated heating systems
- Heaters have to be cleaned regularly in order to ensure that heat transfer remains effective
- Access to heaters integrated into the digester or the structure is very difficult, if not impossible
- Comply with applicable health and safety regulations for working inside the digester
External heat exchangers
Very good accessibility for maintenance and cleaning
Machinery for mixing in the digester
Submerged-motor propeller-type agitators
- In some cases difficult, because the motor has to be lifted out of the digester
- Maintenance hatches and engine-extraction hatches have to be integrated into the digester
- Comply with applicable health and safety regulations for working inside the digester
Long-shaft agitators
- Motor maintenance is straightforward on account of siting outside the digester; no need to interrupt the process
- Repairs to propeller and shaft difficult, because they have to be taken out of the digester or the fill level inside the digester has to be lowered
- Maintenance hatches have to be integrated into the digester
- Comply with applicable health and safety regulations for working inside the digester
Axial agitators
- Motor maintenance is straightforward on account of siting outside the digester; no need to interrup in the process
- Repairs to rotors and shaft difficult, because they have to be taken out of the digester or the fill level of the substrate in the digester has to be lowered
- Maintenance hatches have to be integrated into the digester
- Comply with applicable health and safety regulations for working inside the digester
Paddle/paddle-wheel agitators
- Motor maintenance is straightforward on account of siting outside the digester; no need to interrupt the process
- Repair of paddles and shaft difficult, because the digester has to be emptied
- Maintenance hatches have to be integrated into the digester
- Comply with applicable health and safety regulations for working inside the digester
Pneumatic mixing
- Gas-compressor maintenance is straightforward on account of siting outside the digester; no need to interrupt the process
- Repair of biogas injection equipment difficult, because the digester has to be emptied
- Comply with applicable health and safety regulations for working inside the digester
Hydraulic mixing
Equipment specific maintenance is similar to that of the pumps stated above.
Sediment discharge and removal systems
- Maintenance of permanently installed systems requires emptying the digester, so out-of-tank drives or removal equipment have advantages
- Comply with applicable health and safety regulations for working inside the digester
Gas storage tanks
Maintenance-free to a very large extent.
Flare system
Maintenance-free to a very large extent.
Templates for regular maintenance
Biogas Box
Collection of literature on Maintenance
WEB
Maintenance of a Cogeneration Plant
Biogas plant maintenance at blogspot (for domestic biogas)
Maintenance service provider MT-Energie
References
- ↑ 1.0 1.1 1.2 GIZ, FECC, 2012. Christensen: Operation and Maintenance, Pilot Training for biogas plant technicians Cite error: Invalid
<ref>tag; name "Christensen" defined multiple times with different content Cite error: Invalid<ref>tag; name "Christensen" defined multiple times with different content - ↑ FNR, 2012: Guide to biogas. p. 38.
