Explosion hazards
Explosions can occur if the gas is mixed with sufficient air to form an explosive mixture.
This could occur for several reasons:
— air leakage into the gas system;
— air penetration during refuelling;
— air leakage into a cold gasifier still containing gas which subsequently ignites;
— backfiring from the fan exhaust burner when the system is filled with a combustible mixture of air and gas during starting-up.
Air leakage into the gas system does not generally give rise to explosions. If a leakage occurs in the lower part of the gasifier (as is generally the case) this will result in partial combustion of the gas leading to higher gas outlet temperatures and a lower gas quality.
When the pyrolytic gases in the bunker section are mixed with air (as is bound to happen during refuelling) an explosive mixture can be formed. It is not unusual for this to result in small and relatively harmless explosions, especially when the fuel level in the bunker is relatively low.
Risk to the operator can be obviated if the gases in the bunker section are burnt off through the introduction of a piece of burning paper or the like, immediately after opening the fuel lid. Another possibility is to install a double sluice type filling system.
Air leakage into a cold gasifier and immediate ignition will lead to an explosion. Cold systems should always be carefully ventilated before igniting the fuel.
During the start-up of an installation, the gases are as a rule not passed through the entire filter section, in order to avoid blocking the filters with the tars produced during start-up. The filter may thus still contain air, and after an inflammable gas is produced and led through the sometimes quite voluminous — filter section an explosive mixture can result. If the gas is now ignited at the fan outlet a backfire can occur, leading to a violent explosion in the filter section. It is fox this reason that it is advisable to fit the fan outlet with a water lock.