Volume 1, Issue 12 - November 2009

Transcription

1 selection, and thorough geological and other assessments of the surrounding regions. 1 Volume 1, Issue 12 - November 2009 Invited article Underground Coal Gasification: A Future Clean Coal Utilization Technology for India Preeti Aghalayam, Visiting Associate Professor, Dept. of Chemical Engineering, IIT Madras preeti@iitm.ac.in Introduction UCG refers to the in-situ gasification of coal. It is accomplished by first establishing two vertical boreholes the injection well and the production well. Next, the two wells are horizontally linked within the coal seam using specialized techniques such as directional drilling. Reactant gas mixtures (steam & oxygen) are sent through the injection well, and suitable conditions for the ignition or start-up of the coal reactions is provided. A steady production of combustible gases due to the various reactions occurring between the gases and the coal, is evident at the production well. UCG presents several advantages over conventional coal mining and utilization techniques. The lack of need of mining and transportation results in much savings, especially for coals that contain a large fraction of ash. Furthermore, some of the environmental impacts, such as the production of NO x and SO x due to surface coal processes, are significantly reduced in case of UCG, through the maintenance of a reducing atmosphere underground. Finally, UCG enables the utilization of deep and thin coal seams, which are not accessible for mining, and could provide an efficient carbon capture and sequestration (CCS) possibility. However, UCG possesses some distinct disadvantages as well. UCG is fairly capital intensive, and has been successfully practiced at only a few world-wide locations. The environmental impacts on aquifers situated close to UCG operation, and the potential of surface subsidence are some of the other problems associated with UCG. These problems may only be overcome through proper site Potential for UCG in India India is a traditional coal country, possessing >250 billion tonnes of coal, with >60% of energy needs being met through coal-based technologies. The concerns around the potential depletion of coal reserves in the foreseeable future have been abundant in recent times, alongside the focus on the environmental impacts of coal utilisation. At least 30 % of Indian coal reserves are situation at a depth > 300m below the earth s surface (see Table 1). Furthermore, the rank or quality of Indian coals is usually low, with high ash content. Thus, the economical mining and utilization of this valuable, deep, coal resource is not feasible through conventional techniques. Table 1: Indian coal reserves at various depths (Khadse et al., 2007) It is believed that UCG will play a unique role in enabling us to utilize these reserves. At this time, ONGC, GAIL, and RIL are some of the companies that have expressed interest in UCG in India. ONGC has recently proposed a pilot UCG station, producing 5.5 lakh m3/day of syngas, by the end of 2010 at Vastan near Surat in Gujarat (Business Standard, Aug 21, 2009). The norms & guidelines for the practice of UCG have been recently notified by the coal ministry (on July 13, 2009). It seems logical and evident that in the near future, UCG will emerge as a major clean coal utilization technology capable of providing significant impact in our country. Research in UCG Due to the worldwide interest in UCG practice, academic research in the field has also increased enormously in recent times. The combination of phenomena that exists in the underground coal

2 gasification seam presents an extremely complex situation. Field-scale experiments, though invaluable in providing insight, are very difficult to envisage, and expensive as well. Laboratory-scale experiments, on the other hand, are feasible, but their scalability is usually questioned [Upadhye et al., 2006]. Mathematical modeling and simulation of the UCG phenomena is expected to bridge the gap between lab-scale experiments and field-practice. However, since UCG is a complex process, and involves phenomena occurring at different length and time scales, robust mathematical models encompassing all aspects of UCG are as yet unavailable in literature. In general, an approach wherein the UCG cavity is treated as a natural chemical reactor, with reactions, mass and heat transport, solid wall movement, liquid water influx, etc. taken explicitly into account through appropriate terms in the balance equations, is gaining popularity. Particularly interesting is the phenomena of cavity growth which is at the core of UCG. Typically, directional drilling techniques establish an initial link between the injection and the production well in the chosen coal seam. Igniting mixtures, and reactant gases next initiate the reactions in the seam. Due to the steady consumption of solids (coal & char), and the egress of product gases, a cavity (typically of a hemi-spherical shape, when the injection point is maintained at the bottom on the seam), is formed, and evolves in shape as the reactions proceed. This is also evident in the schematic of Fig. 1. known to disengage from the unreacted seam and fall through the cavity, encountering a highly reactive atmosphere along the way); and so on. At the UCG research group at IIT Bombay, several phenomena relevant to this fascinating problem are being studied (see Fig. 2). A detailed thermogravimetric analyser (TGA) based study to establish intrinsic reaction kinetics for chosen Indian coals is underway [Khadse et al., 2008]. A fully instrumented fixed bed reactor is also being used to study the pattern of reactions, and also the interplay of transport and kinetics. Several mathematical modeling and simulations exercises have been undertaken. A simple one-dimensional process model, based on kinetics, has been demonstrated to give interesting insights into UCG, while predicting lab-scale experimental data [Khadse et al., 2006]. A detailed flow patterns study using Computational Fluid Dynamics, has been conducted, and, the information used to develop an equivalent reactor network [Daggupati et al., 2009], for robust performance predictions. Finally, in recent laboratory-scale experiments, the shape of the coal combustion cavity has been established, and demonstrated to be strongly controlled by the mass transfer rate of the reactant gases [Daggupati et al., 2009]. 2 Figure 2: Mathematical modeling of UCG Figure 1: Schematic of UCG The size (and in more general terms, the threedimensional shape) of the cavity at any point of time is indicative of the progress and efficiency of the gasification process. The quality of the product gas obtained at the production well is strongly dependent on the underground cavity growth phenomena. Operating conditions selection therefore requires a continuous knowledge of cavity shape/size. The cavity growth is expected to be governed by: reactions (combustion, gasification, or both); transport phenomena (especially mass transport of reactant gas to the reacting coal/char face); thermomechanical failure properties or the phenomenon known as spalling (pieces of coal are Summary Underground coal gasification (UCG) displays significant potential as a future coal utilization technique, especially for the deep, low ranked coal seams found in several locations in India. While the UCG process is inherently extremely complex, an approach involving treating the reacting cavity as a natural chemical reactor, involving several interlinked phenomena, represents an important advance. In the UCG research group at IIT Bombay, research aimed at in-depth comprehension of UCG has reached a stage of maturity. The predictive process models emerging from the group are expected to hugely benefit the design, optimization and control of UCG field trials and commercial installations in India. References

3 Daggupati S., Mandapati, R. N., Mahajani, S. M., Ganesh, A., Mathur, D. K., Sharma, R. K., and Aghalayam, P., Laboratory studies on combustion cavity growth in lignite coal blocks in the context of underground coal gasification, Energy (under review), Daggupati S., Mandapati, R. N., Mahajani, S. M., Ganesh, A., Sapru, R. K., Sharma, R. K., and Aghalayam, P.,,, Underground coal gasification performance predictions using compartment models, presented at the International Pittsburgh Coal Conference, Oct 2009 Upadhya, R., E. Burton, and J. Friedmann, Science and technology gaps in underground coal gasification, Technical Report UCRL-TR , Lawrence Livermore National Laboratory, University of California, Berkeley, CA, Khadse, A. Underground coal gasification: Kinetics and process modeling, Ph.D. Thesis, Dept. of Chemical Engineering, IIT Bombay, Mumbai, India, Khadse, A., M. Qayyumi, S. M. Mahajani and P. Aghalayam, Reactor model for Underground coal gasification channel, International Journal of Chemical Reactor Engineering, V4, A37, 2006 Khadse, A, Qayyumi, M., Mahajani, S.M., Aghalayam, P., Underground Coal Gasification: A New Clean Coal Utilization echnique for India, Energy, 2007, 32, The UCG Group at IIT Bombay consists of Profs. Anuradda Ganesh (Energy Systems & Engineering, Principal Investigator); Sanjay Mahajani & Preeti Aghalayam (Chemical Engineering, Co-PIs), Phd Scholars Sateesh Daggupati & Ramesh Naidu, and several dedicated staff & students. We welcome your inputs and visit to the UCG lab, situated in the Aero Engg Annex at IITB, which has been set up through sponsored project funds from the IRS, ONGC. Energy Research at IITM- 4 Research on Biodiesel Combustion in Engines Pramod S Mehta Internal Combustion Engines Laboratory Department of Mechanical Engineering, Indian Institute of Techology Madras psmehta@iitm.ac.in Introduction The engine technology today is experiencing a rapid pace of development. The combustion process and systems of reciprocating internal combustion engines remain at the center of various technological innovations taking place in automotive industries world-over. These developments are primarily driven by the concerns on the depleting fuel resources and the adverse environmental impact of the species emitting from engine exhaust. There are intense activities in the area of alternative fuels for internal combustion engines. An attractive feature of an alternative fuel is its emission reduction potential. From this standpoint the fuels like natural gas, alcohols, biodiesel and hydrogen have attracted considerable attention to replace the fossil fuels. The processed vegetable oil i.e. bio-diesel has emerged as an attractive alternative for diesel fuel considering its renewable nature, better ignition quality, comparable energy content, higher density, higher safety due to higher flash point, non-toxic character of its exhaust emissions, almost zero sulfur content, cleaner burning and acceptability in diesel engines without any hardware modifications [1, 2]. Biodiesel is an oxygenated fuel which comprises mono-alkyl esters of long chain fatty acids derived from vegetable oils and animal fats by transesterification process. The biodiesel fuels are carbon neutral and are directly miscible with diesel fuel. They considerably reduce exhaust smoke emissions but have slightly higher NOx emissions. The nonedible oils like Jatropha, Karanja, Mahua, Neem etc are the preferred sources for producing biodiesel fuel. Being a tropical country, India has a large potential to produce Jatropha curcas plant [3]. Karanja (Pongamia Pinnata) can be cultivated on any type of soil that has low moisture demand [4]. The straight vegetable oil molecules are composed of triglycerides with non-branched chains of different lengths and different degree of saturation [5]. The differences in physical properties of biodiesel fuel derived from different vegetable oils cause some difference in their performance potential due to differential effects on spray and combustion related processes [6]. The ongoing research on use of Jatropha and Karanja methyl esters in compression ignition engines concerns: Generating data related to performance, combustion and emission characteristics of neat biodiesel viz Jatropha and Karanja and their blends with diesel fuel in a compression ignition engine understanding the effect of biodiesel fuel structure and composition on the performance, combustion and emission behavior of compression ignition engine predicting the properties of biodiesel fuels based on their fatty acid composition establishing correlations for biodiesel fuelled engine processes like ignition delay, combustion duration and fuel mass burning rate 3

4 controlling nitric oxide emissions using biodiesel - methanol blends analyzing biodiesel combustion through detailed CFD and kinetics modeling investigating the effects of storage stability of the biodiesel fuel on engine processes and performance. EXPERIMENTAL FACILITY A well instrumented engine test facility (see Fig 1) is built around four cylinder turbocharged in the laboratory to conduct experimental investigations. Fig. 1: Pictorial views of test-engine setup and instrumentation The important outcome of the current research efforts include: Performance of Biodiesel and its blends vs fossil Diesel Fuel in Diesel Engine.Fig. 2 shows the typical comparison of engine combustion, performance and emission characteristics of neat Karanja (KME) and Jatropha (JME) methyl esters with base diesel at an engine speed of 2000 rpm. These results suggest that There is an advanced start of injection up to CA and consequent early start of combustion for biodiesel fuels (refer Fig. 2a) due to their higher density/less compressible nature compared to base diesel. There is a slight increase in ignition delay (refer Fig. 2b) and decrease in combustion duration (refer Fig. 2d). The magnitude of peak cylinder pressure increases for biodiesel fuels and the rate of increase is significant at higher loads (refer Figs. 2c). There is an increase in brake specific fuel consumption (refer Fig. 2e) and slight decrease in thermal efficiency (refer Fig. 2f) of biodiesel fuels primarily due to their lower energy content. There is not much difference in the exhaust Carbon Monoxide (CO) concentrations for both diesel and biodiesel fuels (see Fig. 2g). The unburned hydrocarbon and exhaust smoke emissions are significantly decreased for biodiesel fuels as compared to base diesel (refer Figs. 2g and 2h) whereas nitric oxide emissions are increased for biodiesel fuels (refer Fig. 2h) The increase in nitric oxide emissions with biodiesel fuel are attempted to be minimized by blending 10% methanol with biodiesel. The typical results comparing effects of Karanja biodieselmethanol blend (B90M10) with neat Karanja biodiesel (B100) at 1000 rpm engine speed are shown in Figs. 3. The following facts are observed: - There is a delayed start of injection and an increased ignition delay (refer Fig. 3a) primarily due to lower density/higher compressible nature and poor ignition quality of biodieselmethanol blend compared to neat biodiesel. The magnitude of peak cylinder pressure decreases (refer Fig. 3b) for biodieselmethanol blend due to higher latent heat of vaporization of the blend and there is slight increase in brake thermal efficiency due to wider flammability limits and lean burning characteristics of biodiesel-methanol blend. 4 g h

5 5 a e b f c d Fig. 2: Comparison of engine combustion, performance and emission characteristics of Jatropha and Karanja biodiesel fuels with base diesel Fig. 3: Comparison of (a) brake thermal efficiency and (b) nitric oxide and exhaust smoke emissions for biodiesel and biodiesel-methanol blend The nitric oxide and exhaust smoke emissions decrease significantly for biodiesel-methanol blend (refer Fig. 3b) due to higher fuel bound oxygen of the blend. Besides these basic performance studies, the research efforts led to evaluating the effects of long storage of biodiesel on engine performance, combustion and emission characteristics have also been evaluated. A generalized, simple and accurate method for estimating thermo physical properties of biodiesel fuels derived from source vegetable oil of varying compositions has been successfully evolved. A new methodology has been proposed for estimating the lower heating values of biodiesel fuels using bond energy code in conjunction with KIVA3V CFD package is being pursued. Brake thermal eff. (%) B100 B90M10 a bmep (bar) Fig. 3a: Comparison of (a) brake thermal efficiency method. The modeling of the biodiesel ignition and combustion processes using CHEMKIN

6 NO (ppm) B100-NO B100-Smoke b B90M10-NO B90M10-Smoke bmep (bar) Smoke (BSU) Fig. 3b Comparison of nitric oxide and exhaust smoke emissions for biodiesel and biodiesel-methanol blend Acknowledgement: This work is the result of the efforts of Mr K Anand, Research Scholar towards his Ph D thesis. REFERENCES 1. Ma, F., and Hanna, M. A. (1999) Biodiesel production A review, Bioresource Technology, 70, pp Srivastava, A., and Prasad, R. (2000) Triglycerides-based diesel fuels. Renewable and Sustainable Energy Reviews, 4, pp Mohibbe Azam, M., Waris, A., and Nahar, N.M. (2005) Prospects and potential of fatty acid methyl esters of some non-traditional seed oils for use as biodiesel in India, Biomass and Bio Energy, 29, pp Srivastava, P.K., and Verma, M. (2008) Methyl ester of Karanja oil as an alternative renewable source energy, Fuel, 87, pp Rao, P.S., and Gopalakrishnan, K.V. (1991) Vegetable oils and their methyl esters as fuels for diesel engines, Indian Journal of Technology, 29, pp Rakopoulos C.D., Antonopoulos K.A., Rakopoulos D.C., Hountalas D.T., and Giakoumis E.G. (2006) Comparative performance and emissions study of a direct injection diesel engine using blends of diesel fuel with vegetable oils or bio-diesels of various origins, Energy conversion and Management, 47, pp Events Dr. Srinivas Bette, President and CEO, Reliance International E and P, Dallas, USA gave a talk on Trends in Oil and Gas Exploration and Production and its influence on the Indian Energy Scenario on 03 Nov Prof M.S. Ananth, Director, presided. A large number of students and faculty listened to the very interesting and informative lecture followed by a lively interaction. Earlier Dr. Bette visited the Dept of Ocean Engineering for a discussion on the M Tech (Petroleum Engineering) programme. Dr Bette is an IITM alumnus (BT Chem 1976). A presentation on A Possible Solution to the Rural Energy Problem was delivered on the 13 th Nov by a team of students from IITM who won the national contest on The GE Edison Challenge. The winning team, which was awarded a cash prize of Rs 5 lakhs, consisted of : Srinath Ramakkrushnan, Mechanical Engg. Ashwin Ramesh, Mechanical Engg Midhun Salim, Electrical Engg Kaushik Anand, Chemical Engg Aditya Harit, MA in Developmental studies ANNOUNCEMENT The Energy Forum will observe The National Energy Conservation Day on the 13th and 14 December as was done last year. Details will be sent shortly. Please send in your suggestions. Your response requested. Please suggest topics and names of experts for the monthly lecture series. Also please suggest other activities that can be arranged in lieu of the monthly lectures. 6 For comments, suggestions and contributions write to kolar@iitm.ac.in or scrajan@iitm.ac.in