Vehicle gasifier systems must be of compact and lightweight design. To achieve this, some sacrifices of efficiency may be necessary. More frequent servicing may also be required. Vehicle gasifier systems, for instance, are almost exclusively fuelled manually. The compact designs of ash pits and filters make fairly frequent cleaning necessary.
The lightweight design will imply minimum use of material which as a consequence leads to a shorter lifetime for parts exposed to corrosion. This may appear to be a serious shortcoming for use in stationary applications, but it must also be understood that lightweight and compact designs bring some advantages, which for some stationary applications will outweigh their negative consequences. Lightweight and compact designs can be built more cheaply and with less well equipped workshop facilities. Transport to the site will be simpler and cheaper. Site assembly work can be virtually eliminated, since the power plant can be built and transported as a unit. All this will result in lower capital costs.
Finally, the choice of technology will depend on an economic evaluation. It is then quite possible that vehicle type systems will turn out to be the most economic choice for some applications. Bearing in mind the special features of such systems, it appears reasonable to assume that they will be competitive under the following circumstances:
- low labour cost (more time required for operation and service is then not so important);
- short to intermediate annual operating time (low capital cost is then important, frequent service and maintenance less important);
- local manufacturing desirable (vehicle type systems require less well equipped workshops);
- remote sites (transport costs and site assembly costs can be reduced with compact and lightweight systems);
- mobile plant needed (compact and lightweight plants can be trailer mounted).
Two stationary power plants using vehicle type systems similar to the standard designs described in section 3.2 have recently been built and operated in Sweden.
One with a power output of abut 30 kW has been built by "Gotland Gengas" and is used at the Royal Institute of Technology in Stockholm by the Beijer Institute-for tests with various fuels. No operational problems have been encountered with wood as fuel.
The other stationary plant is a prototype for a commercial plant with a power output of 40 kW built by Elektromatic Power Generation AB. It has been operated for several hundred hours at a sawmill, using wood chips as fuel. Modifications mainly aimed at a simpler control system are now being considered.
The experience gained from the operation of these two plants appears to verify that vehicle type systems can also operate satisfactorily in stationary applications. Whether such systems are more or less economic than systems designed specially for stationary use, such as those described in Chapters 4 and 5, or not, can only be established through more extensive operation under field conditions and will probably depend on the particular circumstances of each case.