TABLE OF CONTENTS The effect of gasification pressure and temperature on gas composition, yield and cold gas efficiency was discussed in Section 2.3.1. There are other aspects to consider, however, when deciding on the values of these parameters in a process, and these are discussed here.
The pressure in a gasifier is generally based on the requirements of processes down-stream of the gasifier. This requirement is easily met when the downstream process is a combined cycle (CC) that typically requires a pressure in the gasifier of 20 40 bar. Other processes, such as methanol or ammonia synthesis, require much higher pressures of 50 200 bar, and thus compression of the synthesis gas.
In principle, it looks more attractive to pressurize the feed to a gasifier than to pressurize the syngas. However, it should be realized that most of the advantages in terms of equipment compactness and lower compression energy are already obtained when gasifying at a pressure of 15 25 bar. Moreover, where the feedstock is a solid, such as coal or biomass, pressurizing becomes more and more complicated at higher pressures. With air-blown gasification, there is in principle less reason to prefer pressurization of the blast, since the savings on syngas compression are much less due to the large percentage of inerts in both the blast and the product gas.
For high-temperature entrained-flow gasifiers, this theoretical argument of pressurizing the blast components remains valid for quite high pressures of 100 150 bar because of the low methane content in the gas.
