Experiences related to service, maintenance and equipment failures
For an economic assessment of straight wood gas or dual fuel operation of farm tractors and other vehicles, data for extra service time, as well as costs and time required for maintenance and repair are of great importance.
Records on service and maintenance intervals as well as equipment failures have been kept for the vehicles tested by the National Swedish Testing Institute for Agricultural Machinery,
see Tables 3.17 and 3.18. There are variations between different vehicles and, rather than presenting here the experiences for the two vehicles reviewed in detail, it has been preferred to present integrated experiences based on the operation of several of the vehicles. Table 3.18 shows approximate service intervals and the approximate time required for the service jobs.
Assuming that the vehicle is used eight hours per day, the service time required for the gasifier system can be estimated as 15 — 25 minutes per operating hour, including refuelling stops.
The approximate repair intervals for different critical components are given in Table 3.18, which is based on experiences from practical operation of several vehicles. These experiences are not necessarily representative of what would be found if the technology were in widespread regular use. The present experiences may be biased in a negative direction because the systems tested were to a large extent first or second generation prototypes — they were also manufactured with the cheapest materials which could reasonably be used. Commercial products in regular use could be expected to show longer lifetimes if they are maintained and operated like the prototypes.
The experiences may, however, also be biased in a positive direction because the operators of the test vehicles have been more keen and interested in the functioning of the system than the average operator might be if the technology were widely used. Most of the service and maintenance tasks are dirty. This may lead to neglect by some operators. There are also some difficulties associated with the assessment of the failure rates which could be expected for other operating situations. Some of the failures, like chafing of filter bags, and cracking of throat plates are clearly related to the number of operating hours. Others such as corrosion damage could be more dependent on the actual age of the component.
The repair costs for the prototype systems are probably not at all representative of the costs which would be experienced in practical operation. Mass produced spare parts would be much cheaper than the spare parts made specially for the prototypes.
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Table 3.17 Service and maintenance intervals for vehicle gasifier systems in practical operation
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V Done during refuelling stop
2/ Can normally be done as part of daily preparation. Time given for that includes these tasks.
3/ The cleaning interval depends on the pressure loss accepted and the size of the filter surface relative to the gasflow.
4/ Cleaning required after gas filter failures. Frequency estimate based on observed failure rates for filter bags.
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Table 3.18 Lifetimes of some critical components between repair or replacement according to practical operation experiences
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It does not seem unreasonable to assume a lifetime of about six years for the gasifier system in general, and a repair cost of five per cent of the capital investment per 1,000 hours of operation. The repair cost is estimated on the assumption that the filter bags must be replaced every 500 — 1,000 hours, and that repairs to the parts of the system exposed to high temperature or corrosive condensates are necessary with about the same frequency.