(349a) Thermochemical Conversion of Coal and Biomass to Liquid and Gaseous Fuels

Thermochemical
Conversion of Coal and Biomass to

Liquid and
Gaseous Fuels

Abstract

Venkata Abhijit
Bhagavatula¹, Naresh Shah²
and Gerald Huffman²

 Consortium
for Fossil Fuel Science, Department of Chemical and Materials Engineering,

University
of Kentucky, Lexington, KY ? 40508

Introduction:

The
use of biomass as a renewable source of energy has been increasingly gaining
importance over the past few years. The growing concerns over green house gas
emissions, along with the need for energy independence have accentuated the
need for using alternative sources of fuel and chemical feedstocks. A flowchart
illustrating the process of converting solid coal/biomass into gaseous and
liquid fuel is shown in Figure 1.

Figure 1. Flowchart
illustrating the process of converting solid coal/biomass into gaseous and
liquid fuel.

Gasification
is the thermochemical process of converting a solid carbonaceous source such as
coal or biomass into synthesis gas (CO + H₂) which is used as a
feedstock for producing fuels and chemicals. Gasification, generally done in
the presence of mixtures of air/pure oxygen and steam at temperatures ranging
between 600 ºC and 900 ºC, produces a gaseous mixture of hydrogen, carbon
monoxide, steam, methane and light hydrocarbons along with some undesirable
effluents such as inorganic particulates and condensable organic vapors or
tars, as they are commonly known.

Using biomass alone as
the gasification feed greatly reduces the green house gas emissions but the
process not only involves higher operating costs but also produces higher
amount of tar when compared to that of coal. The high tar content of product
gases from biomass gasification is a major and widely recognized problem. These
high tar contents arise mainly from the lower temperatures and shorter
residence times in gasifiers constructed for biomass processing compared to
those designed for coal gasification. Tar yields from ligno-cellulosic biomass
materials tend to be considerably higher than tar yields from coals. Co-gasification
of blends of coal and biomass to produce syngas (CO + H₂), which in
turn can be used as feedstock for processes such as Fischer-Tropsch Synthesis
used for producing liquid fuels, is a major area of research.

The
main objective of this research is to perform the co-gasification of different
blends of coal and biomass in a fixed bed reactor and analyze the products in
order to achieve high concentration of synthesis gas. Two different types of
coal namely, sub-bituminous and lignite, and different types of biomass such
as, pine and poplar, have been used for the co-gasification process. Using
thermogravimetric analysis, the pyrolysis characteristics of mixtures of coal
and different biomass samples have been analyzed. The effects of various coal
and biomass blends, temperature, pressure and oxygen to steam ratio, in
addition to the particle size effects, on the gasification products have been
studied thoroughly. 

The energy content of
the gas produced through gasification depends on numerous factors, such as the
oxidizing agent, reactor type, fuel type and form, etc. The oxidizing agent can
be chosen as air, oxygen, steam, or a mixture of these. When air is used, the
resulting gas has a low calorific value. This can be increased by using oxygen
or steam but in the latter case sufficient heat should be provided because
steam gasification is an endothermic process.