Spontaneous Combustion
As in a conventional PC power plant, safety precautions in coal storage and handling are essential to avoid spontaneous combustion. This applies equally well to other feedstocks such as biomass and certain types of waste. The key in particular is to prevent fines from drying out, so that a first-in first-out inventory policy must be part of the safety procedures.
Besides the fuel itself, there are other potential sources of spontaneous combustion. Particular attention must be paid to FeS which may form as a product of corrosion. Another potential source is incorrect handling of catalysts, particularly unloading spent catalyst, which may not have been adequately oxidized in situ. Acting in strict conformity with the catalyst vendors’ procedures is important.
9.3.2 Toxic and Asphyxiating Materials
Apart from the main syngas component, carbon monoxide, there are many other toxic gases present in a gasification complex, particularly if the end product is a chemical. Typical toxic gases present in synthesis gas can include compounds such as H2S and COS as well as ammonia and HCN. The design of a plant must take account of this, and personnel must be trained in their safe handling. There are many public sources of safety information available on material safety data sheets. Many of these are available from Internet sources such as www. ilpi. com/msds, which has links to many international source sites. An up-to-date data sheet should always be available with the safety officer or other member of staff responsible for safety training.
Nitrogen. It may come as a surprise, but a large part of the accidents occurring in gasification plants are due to nitrogen that is produced as a (by-)product from oxygen plants and used for blanketing and transport of coal and further as a diluent for the fuel gas. In this latter function it reduces the stoichiometric adiabatic flame temperature and as a result the thermal NOx.
The problem with nitrogen is that contrary to the fuel gas it has no smell, and even more problematic, it leads very fast to unconsciousness. Good ventilation of the plant is a very efficient precaution. Building a gasifier inside a closed structure because it may look better from a distance can be dangerous. Not only because of nitrogen, but also because we deal with pressurized gases containing CO, H2S, COS, HCN, and NH3. If the plant has to be visually enclosed, the best alternative is to have louver walls that guarantee good ventilation.
CO2- Where concentrated C02 streams are present, one should be aware of its asphyxiating properties and the fact that it is heavier than air. The potential danger is not only because of leaks and open valves. Also, the gas in the stacks through which the C02 is vented should have sufficient buoyancy by ensuring elevated temperatures. For all large quantities, dispersion calculations should be made.