Gasification Of High-ash Coal Research Articles

Design and Development of a Novel Hybrid Gasifier for High Ash Content Coal as feed stock

India has large proven reserve of coal but most of the coal has large quantity of ash. Utilization of this high ash content coal is again a verychallenging task. Presently, gasification of high ash coals has not yet been in application due to the difficulties arising from the ash handlingprocesses. In this work an attempt was made to design a partially fluidized bed reactor that can handle 30 kg/hr coal as a feedstock. By usingan appropriate design procedure a complete design of a hybrid gasifier was studied deeply. The major aim of present research is todetermine the air flow rate for proper gasification, reactor diameter and reactor height, feed particle diameter, nozzle orientation and numbernozzles, reduction zone diameter and height. Experiments were carried out with feeding rate of 9.8 kg/hr with high ash content coal having39.83% ash. Satisfactory results have been found during experiments. The average producer gas generation during trial run was found to be29.8 Nm3/hr while average calorific value of producer gas was about 4500 kJ/Nm3. The work described here favours us understand the realgasification process for high ash content coal and thus facilitates the industrial application of gasification technology.

Effect of Char Temperature on CO2 Gasification of High Ash Coal and Biomass

AbstractInformation on comparative gasification reactivity of high temperature chars in CO2 with high ash coal (C), sawdust (SD) and rice husk (RH) under identical condition is important for clean energy development drive particularly in countries like India, where energy matrix is dominated by coal and introduction of larger quantity of biomass in energy‐mix is attracting global interests. Therefore, TGA‐studies on char‐gasification reactivity using CO2 as a gasifying agent were performed at temperatures 850–1000 °C. In case of coal and RH‐chars, CO2 reactivity found to increase with increasing the BET surface area and reverse trend was observed with SD‐chars. Both the biomass‐chars showed increased specific micro pore surface area with increasing char preparation temperature through t‐plot analysis, still keeping unusual behavior of CO2 reactivity of SD‐char unexplained. The estimations indicating the presence of catalytically active alkali and alkaline earth metals in substantial quantity is only important criteria found to explain the decreasing trend of gasification reactivity of SD‐char prepared at various temperatures despite the increase in surface area. Catalytic activity of the components decreases with the rise in char preparation temperature. Kinetic analysis reveal that activation energy values of SD‐chars varied in the range123–182 kJ mole−1, whereas those for coal‐ and RH‐chars remained in the range 204–214 kJ mole−1.

On the problem of obtaining extra hydrogen-containing synthesis gases during gasification of high-ash coal using iron-containing slags

In the dumps of power plants of the Republic of Kazakhstan, only from the combustion of Ekibastuz coal, ~ 300 million tons of ash have been accumulated, with an annual release of up to 30 million tons. Up to 200 g/t of gallium, germanium, 1 g/t of gold, 4% of zinc, 1% of lead, 0.3% of cadmium and other elements are lost with ash. The work is aimed at unit creation to obtain hydrogen-enriched water gas from ekibastuz coal with the production of Zn, Ga, Ge sublimates, copper-containing cast iron, slag wool and/or cast stone, when joint processing of iron-zinc-contained slag and ash-cinder wastes of thermal power plants.

CO2-O2 dry reforming based underground coal gasification using low and high ash Indian coals

CO2-O2 based underground coal gasification (UCG) is a promising technology for exploiting deep coal seams using a greenhouse gasification agent. High molecular weight hydrocarbons, aromatics, tar etc. in the form of volatile matters in a coal seam possess a significant calorific value. During UCG, these components get evolved as vapours and leave the coal seam without undergoing significant cracking and reforming reactions. As a consequence, a substantial amount of tar is produced along with syngas stream. Alternatively, a novel result of the present study shows that tar-CO2 based dry reforming reactions are catalysed by the pyrolysed carbon zones in the borehole at low temperatures and, these reactions enhanced the calorific value of syngas under a CO2 reactive atmosphere. In continuation of our earlier studies, a detailed experimental study is carried out under single and two stage gasification methods using a typical high ash (42% ash) Indian coal and a low ash (4% ash) North East Indian coal. The effect of feed gas flow rate, molar feed ratio and inherent ash content of the coals on the product gas composition is studied. The results show that two stage gasification of high ash coal produces a medium calorific syngas in the order of 189 kJ/mol, which is equivalent to the heating value of a steam-O2 based UCG syngas. Further, the present study shows that a syngas with a high calorific value of 265 kJ/mol can be produced using the low ash coal under two stage gasification mode. Also, the single stage gasification of low ash coal shows the feasibility of producing a syngas with a medium calorific value of 250 kJ/mol.

CO2 enhanced in-situ oxy-coal gasification based carbon-neutral conventional power generating systems

UCG (Underground coal gasification) is an economic and a viable in-situ clean coal technology in exploiting deep underground coal resources. Sustaining a combustion front in the in-situ gasification of high ash coal is difficult if steam acts as a gasifying medium. In addition, the use of superheated steam causes the transportation problem for deep coal seam. Conversely, these problems could be avoided if CO2 is used as the gasifying medium. In order to implement a CCS ready system in existing plants, the present study investigates the feasibility of integration of CO2/O2 gasification of in-situ coal with conventional power generating systems such as steam turbine and combined cycle power plants performing in a CO2/O2 mode of combustion. The effect of operating pressure and the ratio of CO2/O2 input to an UCG system on the net thermal efficiency of the IGCC system are evaluated. A detailed energy analysis of the CO2 enhanced IUGCC (UCG integrated with the combined cycle) shows a high net thermal efficiency of 41% with CCS (carbon capture and storage) at the UCG operating pressure of 27 bar. IUGST (Integration of low pressure UCG with a steam turbine cycle) system shows a net thermal efficiency of 27% with CCS.

Laboratory scale studies on simulated underground coal gasification of high ash coals for carbon-neutral power generation

Underground coal gasification (UCG) is promising to be an important means of meeting the increasing energy demand in several countries. UCG is inherently an unsteady process since a number of parameters, such as the growth of the cavity, inherent variation in the properties of the coal along the seam, quantity of water influx, ash layer build-up, affect the rates of the homogeneous and heterogeneous reactions occurring therein. In the present study, UCG conditions have been simulated using laboratory scale borehole combustion experiments for three coals and wood block and the effect of some of these parameters is investigated using pure oxygen or oxygen and steam as the gasifying agent. It is shown that, unlike recent reports in the literature, product gas of reasonably high calorific value can be produced on a sustained basis without having to use highly superheated steam as the gasifying agent. Incorporating the results into an integrated underground gasification steam cycle (IUGSC) based power generation system with carbon capture and storage (CCS) shows that the net efficiency penalty for CCS is significantly less than that estimated for conventional systems.

Mineral–Char Interaction during Gasification of High-Ash Coals in Fluidized-Bed Gasification

Indexed with permission from Oboirien, BO, Engelbrecht, AD, North, BC et al. 2011. Mineral-char interaction during gasification of high-ash coals in fluidized-bed gasification. Energy & Fuels, vol. 25(11), pp 5189-5199. Copyright 2011 American Chemical Society

Entrained-flow dry-bottom gasification of high-ash coals in coal-water slurries

It was shown that the effective use of dry ash removal during entrained-flow gasification of coal-water slurries consists in simplification of the ash storage system and utilization of coal ash, a decrease in the coal demand, a reduction in the atmospheric emissions of noxious substances and particulate matter, and abandonment of the discharge of water used for ash slurry. According to the results of gasification of coal-water slurries (5–10 μm) in a pilot oxygen-blow unit at a carbon conversion of >91%, synthesis gas containing 28.5% CO, 32.5% H2, 8.2% CO2, 1.5% CH4, the rest being nitrogen, was obtained. The fly ash in its chemical composition, particle size, and density meets the requirements of the European standard EN 450 as a cement additive for concrete manufacture.

Numerical analysis of the process of combustion and gasification of the polydisperse coke residue of high-ash coal under pressure in a fluidized bed

A numerical analysis of the process of “wet” gasification of high-ash coal under pressure in a low-temperature fluidized bed has been performed. The applicability of the previously developed computational model, algorithm, and program for the case under consideration has been noted. The presence of “hot spots” (short-time local heatings) at different points of the bed has been confirmed.