Use of biogenic solid fuels for process heat
Compared with conventional heaters, which operate with gaseous or fluid fossil fuels, biomass plants use organic solid fuels, e.g. sawdust, wood chips, old timber, or material from landscape management to produce hot flue gas. However, depending on their quality, these solid fuels also put high requirements on the plant. This refers to the combustion process, the components, e.g. heat exchanger or heater, as well as to the legal regulations to be met for emissions.
Since the end of the 90s of the twentieth century, many biomass plants have been built to support alternatives to fossil fuels. However, many plants built in the first years still have some initial difficulties. Therefore, the two- and three-pass heaters, often built at that time, have multiple problems. On the one hand, the large amount of occurring ash is the reason for the need to clean the heaters very often (up to 6 times per year). Each time, this causes the plant to be shut down. On the other hand, this ash is a solid material in the flue gas and at high rates of flow, the flue gas behaves like abrasive paper and little by little, the tube coil will be damaged. This especially applies in positions with high rates of flow, e.g. in return parts of multiple-pass heaters. Over a long term, this abrasion will be the reason for the reduction of the wall thickness of the tube coil and at one time or another there will be holes in it. In the worst case, this can cause a large fire. However, in the best case, a longer standstill and extended repair works will be required.