Showing papers on "Carbochemistry published in 2008"

Basic Factors Controlling Coal Quality and Technological Behavior of Coal

Abstract: Publisher Summary Coal is used in processes such as combustion, gasification, and liquefaction and in carbonization for the manufacture of metallurgical coke. Coal and its derivative products are also used as precursors of other materials and in the production of chemicals. There are two characteristics that influence the use of coal: its composition and its rank. Coal composition is, in turn, represented by two essentially independent factors: type and grade. Coal is a heterogeneous material, and evaluation of coal type may be approached on two different levels: the macroscopical and microscopical, both of which form a part of coal petrology. The chapter also details the coal metamorphism, which involves the physical and chemical transformation from peat through bituminous coal through anthracite and meta-anthracite to graphite. It is a function of heat and pressure acting over a period of time. It is also denoted as the coal rank, which is marked by a progressive decrease in moisture and volatile functional groups with a consequent increase in the carbon content of the coal.

Chapter 5 – Coal Gasification

Abstract: Publisher Summary This chapter deals with coal gasification, which is a process that converts carbonaceous materials, such as coal, petroleum, petroleum coke, or biomass, into carbon monoxide and hydrogen. Coal gasification as a power-generation technology is gaining popularity due to the ready global availability of the raw material (coal), as well as positive environmental issues associated with this technology over other combustion technologies. To ensure optimal process efficiency, an in-depth understanding of the coal properties influencing gasification behavior is required. Gasification performance is dependent on coal type and gasifier configuration. Typically, gasifiers are classified according to the type of reactor used and the way in which fuels and oxidant flow. The choice of gasification technology is dependent on a variety of factors, but coal type is generally the least flexible factor and gasification technology selection is typically based on the coal to be processed.

Sintering and slagging of mineral matter in South African coals during the coal gasification process

Abstract: SINTERING AND SLAGGING OF MINERAL MATTER IN SOUTH AFRICAN COALS DURING THE COAL GASIFICATION PROCESS By Ratale Henry Matjie Supervisor: Professor P. Chris Pistorius Department of Materials Science and Metallurgical Engineering, Philosophiae Doctor (Metallurgy)

Direct Coal Liquefaction

Abstract: Publisher Summary This chapter explains coal liquefaction, which is recognized as a competition between hydrogenation to liquid products and destructive distillation that forms solids. The principal objective of coal liquefaction is the production of liquid hydrocarbon distillate products from a coal's mostly aromatic structure to be used as transportation fuels or chemicals. Coal rank and composition are primary factors that influence liquefaction behavior and, although some of that influence may be overcome by increasing process severity or the use of catalysts, these options may be counterproductive in reducing operating expenses. The chapter explains that coals of high total sulfur content are generally derived from high saline, marine peat-forming environments in which bacteria are more active. Contribution of lipid-like organic materials by bacteria to the biomass may have as much impact on total conversion and oil production during liquefaction as sulfur.

Coal-Derived Carbon Materials

Abstract: Publisher Summary This chapter reviews coal as a raw material, which is mainly used for the generation of power and in the iron and steel industry. Coal and its byproducts are also used in alumina refineries, the chemical and pharmaceutical industry, and in other areas such as the manufacture of paper. It is defined that to obtain chemicals from coal, several strategies are reported that include: gasification followed by a sequence of carbon chemistry processes, the conversion of coal via carbonization, pyrolysis, or liquefaction to liquids and tars followed by the conversion of the components of these derived products to higher value products, the direct conversion of coals to chemicals or materials, and the coproduction of chemicals or materials and fuels along with electricity. The chapter is mainly devoted to solid carbon materials derived from coal and coal byproducts, in which the conventional methods of coal petrology play an important role. Other coal-derived materials such as those obtained from the combustion, gasification, liquefaction, and carbonization processes are also described.

Feedstocks and Feedstock Characteristics

Abstract: This chapter begins by describing coal and coke. The composition of coal is very complex, and the types of coal differ considerably. All coal has been formed from biomass. Coal is often classified in terms of its rank, which increases from brown coal to anthracite. Brown coal, lignite and sub-bituminous coals are designated as low-rank coals, whereas higher-rank coals are often called hard coals. There are two methods to analyze coal, namely, the proximate analysis and the ultimate analyses. The proximate analysis determines the moisture, volatile matter, ash and fixed carbon in the coal. The analysis is an essentially practical tool providing an initial indication of the coal's quality and type. For the ultimate analysis, the percentages of carbon, hydrogen, oxygen, sulfur and nitrogen are determined. There are also other elements that are contained in the carbon like chlorine and phosphorous. The heating value of the coal is determined through combustion of the sample in a calorimeter. Other properties like caking and swelling properties, hardness, and density are also discussed. The chapter also discusses liquid and gaseous feedstocks, in which refinery residues are explored. The term “refinery residue” covers a wide range of materials, some of which are solid at ambient temperatures and others that are liquid under these conditions. The most common residues are obtained by thermally cracking vacuum residue or by subjecting it to solvent de-asphalting. Finally, biomass is also discussed along with its properties, production, etc.

Sub-Bituminous Coals Fired in Boiler Designed for Bituminous Coals

Abstract: In the last two decades there has been little capacity added to coal-based power plants. However, much of the existing plants had to comply with the Clean Air Act amendments. Using sub-bituminous coals has become an important solution for emissions compliance due to their unique constituents and combustion characteristics; these coals are often referred to as enviro coals. The considerable advantages of these coals, like Melawan, Adaro or PRB coals, is their low sulfur compared to typical bituminous coals, which makes its burning more economic as scrubbers or other SO2 reduction technologies are not required. Low nitrogen and ash content as well as their high volatile matter are other advantages of these coals. Hence, firing sub-bituminous coals alone or as blends with bituminous coals is deemed economically attractive. Power generation plants were originally designed to operate on a particular bituminous coal. In order to fire sub-bituminous coals or their blends some modifications are required in the firing modes. These modifications may affect boiler reliability and as result to reduction of the power plant availability and hence increasing operation and maintenance cost. In order to prevent such undesirable effects we initiated a study to understand the influence of using sub-bituminous coals on the capacity, limitations of furnace size, heat transfer surfaces, firing systems, pulverizers, fans and airheaters. The present paper discusses issues connected with each of these issues on the combustion system. We also present recommendations for reliable burning of various sub-bituminous coals and their blends in a 575 MW tangentially-fired boiler. For example, we found that firing Indonesian sub-bituminous coals (Adaro and Melawan) considerably reduced NOx (30% reduction) and SOx (reduced to 200 mg/dNm3 @6%O2 ) emissions without post combustion measures. We also tested various blends of sub-bituminous coals with bituminous coals and found positive and negative synergism in these blends with regard to NOx emissions. We used in the present study a series of experiments in a test facility and computational fluid dynamic codes.Copyright © 2008 by ASME

Simultaneous gasification of coals of widely differing degrees of coalification in entrained flow gasification

Abstract: A method for gasification of fuel in an entrained flow of a gasification reactor. The method includes jointly gasifying a mixture of at least two different fuels having different degrees of coalification, including those of differing coal qualities such as brown coals and stone coals. The method also includes pulverizing the coals forming the mixture in specific grain bands and drying the coals forming the mixture to a specific residual water content.

Analysis on the effect of coal quality on coal liquefaction

Abstract: The coal quality index related with coal direct and indirect liquefaction was intruduced in this paper.The influence of coal rank,maceral,reactivity and environment on coal liquefaction was analyzed.And the adaptability of different coal quality to coal liquefaction process was discussed.

Selection and Comment Based on Coal Gasification Process Technology

Abstract: In allusion to the problems how to select the technical scheme for coal gasification and raw coal kinds used for the projects of coal chemical engineering,oil making by coal and olefin hydrocarbon making by coal and so on,author has described the technical characteristics and their advantages and shortages for the various coal gasification processes within the whole world at present;classification was made for the suitable scope of the gasifiers based on the application effect of various coal gasification technologies;author has also presented the problems to be considered during selecting the kinds of raw coals.