Determination of certain properties of producer gas + water vapour mixture

Abstract

The thermo-chemical biomass gasification is a technique by which a combustible gas called Producer Gas (PG) can be generated from biomass. The raw PG can be directly burnt in a gas burner for heating application. If PG is required to be used in internal combustion engines or to be used as a chemical feedstock for the manufacture of various chemicals, then the raw PG must to be cleaned to remove tar, particulate matter and water vapour. Many gas scrubbing methods are available to clean raw PG. Refrigeration is a method in which the raw PG is cooled to a low temperature so that the water vapour present in PG can be condensed and removed from it. Some of the volatile matter also get condensed as tar. The condensed water would wash away a certain quantity of tar and particulate matter, thus helping in their separation from the main PG stream. So, knowledge of specific humidity of PG + water vapour mixture is essential in order to properly design a refrigeration system for treating raw PG, downstream of a large scale biomass gasifier. The cooling load on the refrigeration plant can be calculated precisely from the knowledge of specific humidity of PG + water vapour mixture, mass flow rate of PG and its enthalpy. In this work, a correlation has been developed to determine the specific humidity of PG + water vapour mixture in the temperature range of 20°C - 60°C, at an absolute pressure of 1.013 bar. The composition of dry PG assumed in the present work is CO: 17%, H2: 18%, CH4: 2%, CO2: 14% and N2: 49%. The result has been compared with those of air + water vapour mixture, natural gas + water vapour mixture and martian atmosphere + water vapour mixture which are available in the literature.