Full Length Article Increasing the UCG efficiency by waste heat utilization Alexey Belov a,⇑ , Igor Grebenyuk a , Oleg Danilov a , Andrei Babaev a , Nikolai Kinaev a,b a Far Eastern Federal University (FEFU), Vladivostok, Russian Federation b Strategic Energy Consulting Pty Ltd, Brisbane, Australia article info Article history: Received 15 October 2016 Received in revised form 17 February 2017 Accepted 24 May 2017 Available online xxxx Keywords: Coal Underground coal gasification Well Heat utilization Oxidizing agent Superheated steam abstract The paper presents an improved well steam generator design and the mathematical model for calculating the operating parameters. Well steam generator increases efficiency of underground gasifier by recovery of the flue gas heat and converting it to the superheated steam. Calculations revealed that the heat recov- ery efficiency of the well design increases with coil diameter and does not strongly depend on fossil coal type and composition of gas mixtures of oxygen and air supplied as oxidizing agents. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Underground coal gasification (UCG) is a promising resource- saving environmentally friendly technology, which has great investment potential in the effective development and utilization of coal deposits. As this technology follows the modern trends in the development of efficient resource utilization, it is in the focus of a number of coal companies worldwide. Developments in this area are carried out in Russia, China, USA, Australia and other coun- tries [1–3]. Currently in the world there are various embodiments of the UCG technologies, at a variety of development stages – from pilot projects to commercial operations stage or pilot deployments. However, despite decades of research, development and even examples of successful commercial implementation of the technol- ogy, there are certain technological problems that remain unre- solved. One of them is the problem of a significant loss of heat energy in the process of gasification of coal seam due to a number of factors, such as: heating of rocks, surrounding coal seam; heat- ing and vaporization of moisture contained in coal and in plenum; loss of heat from underground gas leaks; etc. According to the industry experts [4–6] up to the half of the heat generated in the underground gasifier is irretrievably lost to heating the surrounding rocks. This has a negative impact on the technical and economic indicators of work of underground coal gasification plant. Another significant heat loss is associated with the necessity of cooling the syngas in production well on its’ way to surface (outlet of production well). Consequently, the effective utilization of this energy is an important scientific and technical challenge. The approach proposed in this paper does not aim to decrease heat losses in the UCG gasifier itself, and is limited to improve utiliza- tion of waste heat from the cooling of syngas in production well In this paper, we proposed a mathematical model to calculate the parameters of the heat exchanger flue-well steam generator adapted to the basic principles and laws of thermodynamics and heat engineering. We have analyzed the dependence of the amount of heat energy converted into steam on fossil coal type, on the flue gas composition, on coil diameter, and on the temperature differ- ence in the production well. 2. The mathematical model of the heat exchanger in syngas production well in underground coal gasification 2.1. Design of the steam generation well Almost the entire amount of thermal energy contained in coal reserves transports from the underground gasifier to the surface through production well. Of this amount, 80% of the thermal energy is contained directly in the product syngas. Application of effective technological scheme of recycling heat of the exhaust syngas can increase the higher heat utilization com- http://dx.doi.org/10.1016/j.fuel.2017.05.072 0016-2361/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: School of Engineering, Far Eastern Federal University, 10, Ajax Str., Russky Island, Vladivostok, Russian Federation E-mail address: poraen@mail.ru (A. Belov). Fuel xxx (2017) xxx–xxx Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Please cite this article in press as: Belov A et al. Increasing the UCG efficiency by waste heat utilization. Fuel (2017), http://dx.doi.org/10.1016/j. fuel.2017.05.072