Fuel 113 (2013) 287–299
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Fuel
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Review article Coke oven gas: Availability, properties, purification, and utilization in China ⇑ Rauf Razzaq, Chunshan Li , Suojiang Zhang
Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China article info abstract
Article history: The global demand for energy is constantly on the rise because of population explosion, rapid urbaniza- Received 22 August 2012 tion, and industrial growth. Existing energy resources are struggling to cope with the current energy Received in revised form 20 May 2013 requirements. Aside from exploring renewable energy alternatives, available energy resources must be Accepted 22 May 2013 utilized to their maximum potential. Coke oven gas (COG) is highly rated as a valuable by-product of coal Available online 14 June 2013 carbonization to produce coke in the steel industry. Typically, a single ton of coke generates approxi- mately 360 m3 COG. China annually produces 70 billion N m3 COG; however, only 20% of the gas pro- Keywords: duced is utilized as fuel. Disposing COG without an effective recovery and efficient utilization is a Coke oven gas (COG) serious waste of an energy resource and results in environmental pollution. COG is regarded as a poten- COG reforming Methanol synthesis tial feedstock for hydrogen separation, methane enrichment, and syn-gas and methanol production. It Methanation can also be effectively utilized to produce electricity and liquefied natural gas. The availability, properties, purification, and utilization of COG are reviewed in the current study. COG utilization routes are summa- rized in detail, with focus on some major industrial projects in China and other countries that are based on COG utilization technology. Ó 2013 Elsevier Ltd. All rights reserved.
Contents
1. Introduction ...... 288 2. COG properties and purification ...... 289 2.1. COG properties ...... 289 2.2. COG purification ...... 289
2.2.1. NH3 removal ...... 290 2.2.2. COG desulfurization ...... 290 3. COG utilization ...... 291 3.1. COG combustion ...... 291 3.1.1. Direct COG combustion ...... 291 3.1.2. COG combustion for electricity ...... 291 3.2. Direct reduction iron (DRI) production ...... 291 3.3. Feedstock for hydrogen separation ...... 292 3.4. Hydrogen and syn-gas production ...... 293 3.4.1. Partial oxidation (PO) ...... 293
3.4.2. Dry (CO2) and steam reforming ...... 293 3.5. Methanol synthesis ...... 294 3.6. COG tar utilization ...... 294
Abbreviations: COG, coke oven gas; GDP, gross domestic product; BF, blast furnace; Syn-gas, synthesis gas; CV, calorific value; BFG, blast furnace gas; BTX, benzene, toluene and xylene; HCs, hydrocarbons; CHP, combined heat and power; SOx, sulfur oxide; DRI, direct reduction iron; EAF, electric arc furnace; PSA, pressure swing adsorption; WGSR, water–gas shift reaction; PO, partial oxidation; FTS, fischer tropsch synthesis; CPO, catalytic partial oxidation; S/C, steam/carbon; RWGSR, reverse water– gas shift reaction; COx, CO and CO2; GHGs, green house gases; GHG, green house gas; SNG, synthetic natural gas; CNGCL, China Natural Gas Corporation Limited; LNG, liquefied natural gas; CCPP, combined cycle power plant. ⇑ Corresponding author. Tel./fax: +86 10 82544800. E-mail address: [email protected] (C. Li).
0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.05.070 288 R. Razzaq et al. / Fuel 113 (2013) 287–299
3.7. COG methanation ...... 295 4. Overview of COG utilization technology...... 295 5. COG investment and economy ...... 297 5.1. World scenario ...... 297 5.2. China’s perspective ...... 297 6. Concluding remarks ...... 297 Acknowledgement ...... 298 References ...... 298
1. Introduction 60% of the total global coke production. The annual COG produc- tion in China for 2007 was estimated at around 70 billion N m3. The threat of the world’s energy supply by depletion of fossil However, only 20% of the produced COG is utilized as fuel; most fuel reserves, along with rapid industrialization and urban growth, of the gas is directly discharged into the atmosphere, with serious has not only encouraged the search for alternative energy sources, environmental consequences and considerable energy waste. but it has also pushed for an effective and efficient utilization of Developing new technologies to recover and utilize COG from the available ones. Fossil fuels have predominantly been the major en- steel industry is therefore urgently needed [11,12]. In China, the ergy source for industrial, transportation, and domestic use over coking enterprises located near coal mines only recover 24% of the centuries. Approximately 90% of the global energy require- the COG by-product, losing a high percentage of potential energy ments are covered by these sources alone [1]. Global primary en- as well as generating 25 Mt of carbon dioxide (CO2) [8]. Moreover, ergy usage rose by approximately 2.4% in 2007 and is likely to converting COG into more energy-valued products can signifi- increase further in the future, with developing Asian countries con- cantly enhance the energy efficiency of the steel industry in China. tinuously improving their standard of living. The energy demand in COG has been highly investigated as an important source of
China rose by 7.7%, followed by 6.8% and 1.6% in India and US hydrogen (H2), with Japan making some early developments in respectively [2]. For the past decade or so, China has enjoyed the establishing a sustainable H2 production technology from COG most drastic economic growth, with a 10% increase in the gross [12]. Purwanto and Akiyama [13] proposed a simple method of domestic product (GDP). This growth allowed China to recover H2 production from COG. Onozaki et al. [14] performed the partial quickly from the 2007–2008 financial crisis. With such economic oxidation and steam reforming of tar from hot COG to produce H2 and population boom, the energy consumption in China is also at low cost and high efficiency without using any catalyst. H2 on the rise and, more importantly, strongly affects the global en- enrichment in COG can also be achieved through catalytic methane ergy balance [3]. CH4 reforming via catalytic partial oxidation [15]. The use of mem- The energy structure of China has traditionally been dominated brane technology can also lead to synthesis gas (syn-gas) produc- by coal. Although other fuel options have also entered the energy tion through the partial oxidation of COG [12]. The syn-gas setup in the past few decades, coal still plays a leading role in Chi- (CO + H2) produced from COG via various routes, such as partial na’s energy scenario. Model forecasts predicted an annual increase oxidation, steam reforming, or dry reforming, can be utilized to in coal demand by almost 2% for 2010 [4]. With a coal reserve of an produce important organic products, such as methanol [16]. Cata- estimated 5570 billion tons, the third largest in the world, China is lytic co-methanation of CO and CO2 in COG can also be used for regarded as the world’s largest coal producer and consumer [5]. CH4 enrichment. The choice and nature of a catalyst can signifi- For the past few decades, steel has become an icon of modern cantly affect both the activity and selectivity in CH4 production. urbanization and industrial development, with coal serving as The use of both transition and noble active metal supported cata- the backbone of the iron and steel industries. According to the lysts with different oxide supports have been previously reported
World Coal Association, approximately 70% of the total global steel for CO and CO2 hydrogenation to produce CH4 [17–21]. production relies on coal [6]. The steel industry has played an In the current review, we discuss the availability of COG with important role in the economy of China because of its rich coal re- respect to the steel industry and coke gas production, focusing serves, with a rapid growth overtaking that of Japan to become the on China’s perspective. The purification and utilization of COG is largest steel producer in the world. Despite such achievements, largely discussed, and current utilization routes and future techno- the energy efficiency of China’s steel industry is the lowest among logical research and developments in the said field are considered. the major steel-producing countries around the globe. However, COG utilization facilities in China are highlighted, with key research and development are continuously improving the energy efficiency to achieve a sustainable development [7]. In 2004, the average net energy usage for the coking process in China was Table 1 4.3 GJ/t, whereas the international average was 3.8 GJ/t [8]. Mass and energy flow of a typical coke-making plant Coke oven gas (COG), sometimes simply called ‘‘coke gas,’’ is a [10]. by-product of the coke-making process, where volatile coal matter Energy input (42.7 GJ/t coke) is generated as COG, leaving carbon intensive coke behind. Coke is Coal 91.44% a very strong macro-porous carbonaceous material produced by Electric power 0.37% the carbonization of a specific coal grade or of different coal blends Fuel gas (firing gas) 7.61% at temperatures P1400 K. Approximately 90% of coke produced Steam 0.58% from blends of coking coals is used to maintain the iron production process in a blast furnace (BF) [9]. Typically, 1.25–1.65 tonnes of Energy output (42.7 GJ/t coke) Coke 69.63% coal produces a single tonne of coke, while generating approxi- COG 17.92% 3 mately 300–360 m of COG (6–8 GJ/t coke) [8]. Table 1 shows the Tar 2.77% energy balance for a typical coke-making plant along with different BTX 0.98% raw materials and product distribution [10]. In China, the annual Sulfur 0.05% coke output in 2007 was about 335 million tons, or approximately Energy loss 8.65% R. Razzaq et al. / Fuel 113 (2013) 287–299 289 investment groups and companies at the forefront of a constantly Table 3 developing technology. Finally, some concluding remarks are also Heating value of some typical gaseous fuels [25,26]. presented. Fuel type Heating value (MJ/m3) (MJ/kg) 2. COG properties and purification Natural gas 40.6 56.6 Coke oven gas 19.9 41.6 2.1. COG properties Water gas 18.9 21.9 Blast furnace gas 3.9 2.7 Producer gas 5.8 5.2 Before the advent of natural gas, COG was used to meet the domestic energy demand for industrial cities such as Sheffield generation. Compared with the coking facilities around the globe, and Birmingham in England. However, COG was soon replaced coke plants in Germany have acquired the highest technically pos- by CH4. COG is essentially a mixture of combustible gases such sible standards today. However, engineers and researchers are con- as CO, H2, and CH4, and non-combustible ones, including CO2 and tinuously working to increase the overall plant efficiency and N2 [22]. During the coking process, the composition of the released environmental standards [10]. gas may vary depending on the nature of the utilized coal (Table 2). The basic COG treatment process in the steel industry has not Although COG is regarded as a non-standard gaseous fuel, it still significantly changed in several years. Typically, hot, raw COG from has a reasonable energy content and calorific value (CV), which de- coke oven batteries undergoes the following processes prior to NH pend on the nature of coal and the type of carbonization used. With 3 3 and acid gas removal [30,31]: a high H2 content, COG has a CV of 19.9 MJ/m , which is five times higher than that of blast furnace gas (BFG) (3.9 MJ/m3) [8]. Table 3 1. Hot COG is pre-cooled from a large volume of coal tar mixture provides the heating values of natural gas and other synthetic gas- via direct contact with a weak aqueous ammoniacal solution eous fuels for comparison. directly sprayed into the collection system. The hot gases are As previously mentioned, the type of carbonization process sig- cooled to a temperature between 70 and 100 °C using pri- nificantly affects the production of COG and its properties. A low- mary coolers. During this process, approximately 30% of the temperature carbonization process performed at 700 °C produces initial amount of NH and most of the tar components are a semi-coke, resulting in lower COG and ammonia yields and high 3 removed. After utilization, the discharged liquid, also known tar. COG released under this process has a high CV with low H2 as the ‘‘flushing liquor,’’ is recycled for further use. content. High-temperature carbonization produces a high COG 2. The gas is further cooled to a temperature ranging from yield with less tar and high NH3. Moreover, the CV of the generated 28 °Cto30°C using either direct or indirect secondary cool- COG is lower, with a high H2 content [27]. ers. In direct coolers, COG is cooled via direct contact with a counter-current stream of the same ammoniacal solution. 2.2. COG purification The hot spent solution escaping from the unit is cooled using water-cooled coils and again recycled for further The optimization of the industrial COG purification process has use. For indirect coolers, shell-and-tube heat exchangers become highly significant in achieving an efficient, economical, are deployed, with cooling water running inside the tubes and eco-friendly purification. The potential for improvement is and hot COG flowing outside. huge, especially in the adsorption and desorption units of a COG 3. Finally, the cooled COG is passed through an electrostatic purification plant [28]. COG is a complex mixture of various com- precipitator to remove very fine tar droplets. Some facilities ponents; aside from those listed in Table 2, COG also contains other are also equipped with an on-site tar distillation unit. minor constituents, such as NH , hydrogen cyanide, ammonium 3 4. Naphthalene is recovered in a separator unit, followed by chloride, tar components (tar acid gases such as phenolic acid, the removal of light oil. COG is fractionated to recover ben- and tar base gases such as pyridine), and carbon disulfide. Of these, zene, toluene, and xylene (BTX). H2,CH4, CO, and paraffinic and unsaturated gases are useful in the final clean gas composition, whereas small amounts of CO ,N , and 2 2 During the coke-handling, quenching, and screening processes, O are retained in the final gas. The by-product plant should re- 2 ‘‘coke breeze’’ is produced, which can be used either on-site in the move as much of the remaining constituents as possible, both prac- sinter plant or sold as a usable by-product. tically and economically [29]. Traditionally, a coking plant is A COG cooling system with a closed water circulation cycle pre- connected to a network of integrated steel- and ironworks. A BFG vents the escape of pollutants into the atmosphere, which results with low CV is used to heat the coke ovens, and CV is increased from using a cooling tower. The system has low installation costs by the addition of COG. In most energy-efficient facilities, excess and increased efficiency through the use of highly efficient, self- COG is utilized in small energy-intensive processes within the cleaning helical heat exchangers, rather than conventional ones. plant, such as ignition furnace heating, rolling mills, and power Moreover, because COG has no direct contact with the cooling water, recycled water can be directly utilized [32]. Table 2 A conventional process for the COG treatment plant is shown in Composition (vol%) of COG produced during the coke-making process in the steel industry [23,24]. Fig. 1. Water and tar contents are transferred into a crude tar recov- ery unit, and COG is then cooled at around 27 °C. NH3 and hydrogen COG constituents vol% sulfide (H2S) are scrubbed in a scrubbing unit, and benzole is re- H2 55–60 moved and recovered for further utilization. The water used in CH4 23–27 the scrubbing unit is recycled before being re-pumped into the CO 5–8 scrubber. Finally, NH3 is cracked using a catalyst at high tempera- CO2 1–2
N2 3–6 ture and atmospheric pressure into N2 and H2 (2NH3 M N2 +3H2) C2H4 1–1.5 while H2S is obtained as elemental sulfur through ‘‘Claus process’’. C2H6 0.5–0.8 A biological effluent treatment unit continuously recovers and 6 C3H6 0.07 decomposes different hydrocarbons (HCs) and nitrogenous com- H S 63.2E 5 2 pounds [10]. 290 R. Razzaq et al. / Fuel 113 (2013) 287–299
Fig. 1. Schematic diagram of a typical COG treatment process [10].
3 2.2.1. NH3 removal value of 60.5 g/m . Therefore, the use of NH3 to remove H2S from Conventionally, NH3 in COG is removed while in contact with COG has gained considerable attention. The process includes the the gas containing a solution of sulfuric acid to form ammonium capture of H2S using liquid NH3, followed by treatment with acid sulfate, which is then recovered, crystallized, and dried before it gas under the ‘‘Claus process’’ (Fig. 1) to obtain elemental sulfur is sold as fertilizer. More advanced modern processes of NH3 re- which can be sold as a commercial product. China has installed five moval from COG include the water wash process [33]. After COG such units based on this sulfur removal technology from COG. Cer- is cooled to 27 °C in the secondary cooler, the gas is introduced tain advantages associated with this process include zero toxic into the NH3 removal unit equipped with a stripping section. The emissions and the generation of a useful by-product (sulfur) [34]. gas then enters the adsorption section of the vessel, while a portion During COG desulfurization, one-third of the H2S content is first of adsorbed solution is cooled and recycled. Water from the free consumed under partial oxidation according to the following
NH3 stripper is introduced at the top of the absorber. Water from reaction: the stripping section is continuously cooled and recycled, while ex- 3H2S þ 3=2O2 ! 2H2S þ SO2 þ H2OðgÞ ð1Þ cess water is treated in the fixed NH3 stripper before discharge. Lime or caustic soda is used to react with non-volatile acids to re- After the oxidation reaction, H2S undergoes a Claus reaction, as lease the fixed NH3, allowing it to be steam-stripped from the solu- follows: tion. Vapors escaping from both stripping units are passed through a partial condenser to recover and dispose NH3 and other acid 2H2S þ SO2 ! 2H2OðgÞ þ 3=nSn ð2Þ gases. A typical water wash NH3 removal process reduces COG- The reaction is performed between 230 and 250 °C over an Al O NH content from 200–500 g/100 scf to 2–7 g/100 scf [30]. 2 3 3 catalyst.
One disadvantage of the above process is that the high NH3 con- 2.2.2. COG desulfurization tent in acid gas can trigger a secondary route of oxygen consump-
The removal of hydrogen sulfide from COG using NH3 liquor is tion to produce water, N2, and NOx, resulting in low elemental well-established in the coke-making industry and regarded as a sulfur content. Another major drawback includes the poisoning sufficiently developed separation process. According to European of the catalyst by H2S. To overcome this problem, a high-tempera- standards, H2S in COG must be removed to the acceptable residual ture (>1100 °C) catalytic oxidation of H2S is required. The joint R. Razzaq et al. / Fuel 113 (2013) 287–299 291
removal of NH3 and H2S from COG using the Ama-sulf technology thermal heat loss via reinforced sealing and the thermal insulation was thus introduced. This approach involves the partial oxidation of coke oven batteries [40]. Raw COG can be burned on-site for use of H2S and the simultaneous decomposition of NH3 over a Ni cata- in BFs and in coke batteries in the coking process. Otherwise, the lyst at 1100 °C to 1200 °C [34,35]. gas can be used to generate steam for power and electricity.
Another challenge to this process is the imperfect H2S separa- tion from aqueous ammoniacal solution, in which approximately 3.1.1. Direct COG combustion 2% H2S remaining in the stripping solution causes environmental After the subsequent removal of heavy HCs, COG with a heating 3 problems due to SOx emissions [36]. Park et al. [36] studied the value of approximately 18.6 MJ/m , can be effectively combusted selective removal of H2S from COG in the presence of water vapor in small combustion units such as process heaters and boilers. and NH3 over V2O5/SiO2 and Fe2O3/SiO2 catalysts. The catalysts COG combustion results in the generation of very low levels of haz- showed high selectivity toward H2S removal, with low SO2 forma- ardous air pollutants, similar to those generated by the natural gas tion. The results showed a complete conversion of H2S to a mixture combusting unit. COG shares similar combustion properties with of elemental sulfur and ammonium salt. natural gas (e.g., flame temperature), indicating that both gases would result in the efficient destruction of combustible organic 3. COG utilization compounds under optimal combustion conditions [41,42]. In China, some indigenous coke ovens are heated via the direct For both commercial and environmental reasons, particular combustion of COG in a coal carbonization chamber. In the case of importance is given to the utilization of coke-making by-products, machinery ovens, COG is combusted inside a coal carbonization including COG. COG contains approximately 30 wt% tar as heavy chamber, and the coke oven is heated via heat transfer between
HCs and 70 wt% in the form of light gases, including bulk H2 and the chamber walls. Some of the coking coal may be burned during CH4. Conversion of the entire COG (including tar) into lighter fuel the coke-making process because of direct COG combustion in the constituents can in term of figures meet approximately 4.1% of oven [43]. the global demand for electric power generation [37]. To date, dif- ferent on-site and off-site COG utilization routes have been pro- 3.1.2. COG combustion for electricity posed, including energy generation and syn-gas, H2, methanol, In the steel industry, different surplus combustible gases can and CH4 production (Fig. 2). COG at the high temperature of serve as potential feed stocks to generate heat and electricity for 800 °C has continuously attracted increasing attention as one of combined heat and power plants (CHP). A BFG with a low heating the most promising sources of H2. Through catalytic reforming value can be mixed with COG to generate sufficient energy for and water–gas shift reaction (WGSR), the amount of H2 produced power production [44]. The first COG-based CHP system in China from COG will be several times higher than that of the original has been in operation since 2006 at Shandong Jinneng Coal Gasifi- 3 H2 in the feed COG [38]. Over the years, hot COG has been cooled cation Co., Ltd. (Jinneng, China). The system consumes 9700 m /h and cleaned to obtain a number of important chemicals, including COG at a power generating capacity of approximately 1.60 kW h/ toluene, benzene, and other HCs; this process results in valuable m3, with 3.09 kg simultaneous steam production [45]. Fig. 3 shows thermal and chemical energy loss. Therefore, the concept of hot a simplified process in a COG-based CHP plant. COG utilization should be highly considered to address both eco- nomic and environmental issues [39]. 3.2. Direct reduction iron (DRI) production
3.1. COG combustion Conventional BF iron making is popular throughout the world because of the readily available coke and continuous improve- As one of the key discharge products from a coke-making plant, ments in BF technology. BF processes account for almost 90% of hot COG at a high temperature ( 800 °C) carries 20–30% valuable the global total iron production. Although the process is regarded thermal energy. The first step toward COG utilization should al- as highly efficient, it also has some key disadvantages, including ways be the use of such thermal energy and the reduction of the availability of high metallurgical-grade coke and iron ore as
Fig. 2. Potential routes to COG utilization [10]. 292 R. Razzaq et al. / Fuel 113 (2013) 287–299
Fig. 3. Simplified process in a COG-based CHP plant [45].
Fig. 4. A schematic diagram of an integrated COG-based DRI plant in the steel industry [44]. potential feed stocks, high running costs, and the generation of process fuel with hot DRI, before the process fuel is admitted into gaseous pollutants such as CO2 and sulfur oxide (SOx). The direct the reformer. Alternatively, purified COG can be converted into a reduction process can serve as a complementary alternative to iron reformed gas under steam reforming, and the resulting gas can making in the steel industry. The process is regarded as environ- produce DRI (Fig. 4). A mixture of recycled gas from the direct ment friendly, with less dependence on high-grade metallurgical reduction plant and COG is heated in a reducing gas heater and coke. During this process, the reduction of iron oxides is conducted introduced as the reducing gas to the reduction zone of the DRI in a solid state below the fusion temperature of pure Fe. The oxy- reactor. The process is conducted at a counter flow, with an intro- gen is extracted from the iron ores (Fe2O3/Fe3O4) leaving behind duction of O2 and hot tar gas inducing partial oxidation to produce gangue constituents (un-valuable minerals) in the sponge iron, DRI. CH4 from COG is converted to H2 and CO at the bottom of the which must be separated in the electric arc furnace (EAF). Different reduction zone. Gas leaving the DRI reactor is cleaned via CO2 re- reducing gases are used for this purpose, including CO, CH4, and moval to produce tail gas. The resulting DRI may be used in the H2; other carbon-bearing materials may also be utilized [46–48]. BF, in the converter, or in the EAF [10,53]. An increase in the use of DRI processes has recently been observed due to less investment costs as compared to a BF technology 3.3. Feedstock for hydrogen separation
[49,50]. Although DRI produces less amount of CO2 as compared to BF technology, the amounts off-gas emissions are fairly high Efficient, high-performance, and low-cost technologies for H2 calling for a subsequent gas-recycling during the process [51]. production are urgently needed to boost H2 consumption, which CH4 is mainly utilized as a reducing gas for DRI production and is is regarded as a future clean energy source. At present, H2 can be popular among countries with rich natural gas reserves. China re- produced from an extensive range of source materials, including lies on coke-making and BF processes because of its vast coal re- fossil fuels, alcohol, biomass, and some industrial chemical by- serves. Natural-gas-based DRI production technology includes products [54,55]. COG containing 50–60% H2 is a high-potential Midrex and Hyl processes, and the Finmet process, which uses a source of H2, especially in countries with high coke production fluidized bed [46]. and utilization [56]. Joseck et al. [57] estimated the net amount
COG from an existing coking facility can be used as an alterna- of H2 that can be produced annually from COG is approximately tive reducing agent to natural gas in the DRI process for steel pro- 370,000 t/yr. The production is based on the following ratios: coke: 3 3 duction [44]. Ahrendt and Beggs [52] patented a method coal (0.7 t/t), COG: coke (506 m /t), and H2:COG (0.043 kg/m ). At establishing the use of high sulfur-containing COG for the direct present, some on-site coke plants in the steel industry use pressure reduction of iron oxides. The process is based on an in-situ desul- swing adsorption (PSA) technology to obtain H2 from COG. The furization of the reducing gas (COG) via the reaction of sulfur in the process is carried out in a cyclic adsorption-desorption operation R. Razzaq et al. / Fuel 113 (2013) 287–299 293
Fig. 5. Schematic diagram of H2 separation from COG using the PSA system [57].
using different adsorbant materials such as alumina oxides or zeo- the energy and cost input associated with H2 production [71].To lites [24]. Fig. 5 illustrates a typical PSA unit for H2 separation from develop a commercial process for H2 production from COG using COG. Other important H2 separation techniques include cryogenic a membrane reactor, high-temperature modules with gas-tight distillation and membrane separation. PSA and cryogenic distilla- seals operating at 850 °C should be fabricated. The large membrane tion are the two commercially available processes for H2 purifica- area requirement brings additional problems, including sealing tion but they are considered to be highly energy intensive. and the high pressure drop. Therefore, tubular membranes have Membrane separation technique provides an attractive alternative been developed to minimize such engineering obstacles, including to obtain high purity hydrogen using dense metallic membranes. high-temperature seals [72]. Zhang et al. [72] used a high-temper- The process consumes less energy and provides a possibility of a ature membrane reactor system to assess the oxygen permeation more continuous operation [58]. Although large scale industrial flux and the conversion of CH4 in COG. The closed-one-ended application of H2 separation through membrane technology still membrane tube on the stainless steel support was sealed using a needs to be addressed and more economical and environmentally silver-based reactive-air-brazing alloy with 8 mol% CuO. COG, with friendly ways to recover H2 from COG would be required in the fu- a typical commercial composition of 57.09% H2, 28.18% CH4, 7.06% ture [59]. CO, 3.16% CO2, and 4.51% N2, was fed into the membrane reactor that has its annulus region packed with a commercial Ni-based cat- 3.4. Hydrogen and syn-gas production alyst. Air was blown into a smaller tube inside the membrane tube. The membrane reactor was operated at 875 °C. CH4 conversion, H2
H2 rich syn-gas is an important raw material in many industrial and CO selectivity, and oxygen permeation fluxes were deter- processes for the synthesis of different organic chemicals and fuels mined. A CH4 conversion of approximately 95% was achieved, [60–64]. At present, bulk of syn-gas production comes from steam along with H2 and CO selectivity of approximately 91% and 99%, reforming of natural gas and oil through a catalytic reaction [65]. respectively. COG reforming provides an attractive alternative to a less energy Yang et al. [12] also reported the partial oxidation of CH4 in COG intensive and clean syn-gas production [12,44,66–68]. to syn-gas using a Ba1.0Co0.7Fe0.2Nb0.1O3 d membrane in a mem- brane reactor. The reaction was performed using NiO/MgO as the 3.4.1. Partial oxidation (PO) catalyst. The reforming process was successfully performed at PO (oxy-reforming) has been highly investigated as a potential 875 °C with 95% CH4 conversion, 80% H2 selectivity, and 106% CO selectivity. Cheng et al. [39] achieved H2 enrichment from stimu- route to H2 and syn-gas production due to its mild-exothermic nat- ure making the process more economical and less energy-intensive lated hot COG using a combined medium of a membrane reactor equipped with a Ru–Ni/Mg(Al)O catalyst. The technique, utilizing compared with stream reforming [69].CH4 oxy-reforming for H2 enrichment in COG is attracting considerable attention from both the partial oxidation of HCs under atmospheric pressure, resulted the academia and the industry. Moreover, the process can also pro- in twice the amount of net H2 present in the feed gas. The aiding catalyst used in the process exhibited high catalytic activity and in- duce syn-gas (H2/CO ratio 2) considered suitable for methanol and fischer tropsch synthesis (FTS). Although non-catalytic PO to creased the carbon resistance. Corbo et al. [69] studied H2 produc- produce syn-gas is a well established process, the use of catalyst tion through the catalytic partial oxidation (CPO) of CH4 and can significantly reduce the operating conditions i.e. temperature, propane using Ni/Al2O3 and Pt/CeO2 catalysts; both reactions re- pressure and make process more economical. However, additional sulted in high H2 yields. problems associated with catalyst deactivation through carbon deposition and metal sintering should be addressed [70]. Another 3.4.2. Dry (CO2) and steam reforming problem is the high cost associated with pure oxygen supply. To CH4 reforming of COG for H2 and syn-gas production can also be address this problem, a new reformer with mixed ionic and elec- achieved through dry and steam reforming reactions [73,74]. Both tronic conducting oxygen-permeable ceramics is being investi- the reactions are considered to be energy intensive due to their gated and developed. Most recently, ceramic membrane endothermic nature. Dry reforming produces syn-gas with low technology has proven quite effective in air separation and natural H2/CO ratio which is more suitable for the production of higher gas conversion. This technology provides a combination of oxygen HCs. The process contributes towards fixation of two important separation from air and partial oxidation of CH4 in a single unit. GHGs i.e. CO2 and CH4. However, catalytic deactivation through The application of this combined technology significantly reduces carbon deposition is a major problem for such a reaction [70,75]. 294 R. Razzaq et al. / Fuel 113 (2013) 287–299
Coal char proved to be an active catalyst for CH4 reforming, with surpass 32 million tons each year, with high growth rates nearly low carbon formation and high selectivity. Zhang et al. [73] re- matching the GDP. COG with high H2 contents is considered ideal cently investigated the CO2 reforming of CH4 in COG over coal char for a sustainable methanol production. In China, the COG-based (acting as a catalyst) under the following reactions: methanol production capacity of Shanxi reached 2.06 million tons in 2006 [80]. CH4 ! C þ 2H ð3Þ 2 Syn-gas produced from COG partial oxidation, dry reforming, and/or steam reforming is considered highly useful in methanol CH þ CO ! 2CO þ 2H ð4Þ 4 2 2 synthesis. Although steam reforming of COG has been more inten-
The reaction operates at 700 °C to 1200 °C, and nearly 100% CO2 sively studied compared to dry reforming, the latter has some conversion was attained at approximately 1065 °C. Fidalgo et al. advantages over the former, including energy savings resulting
[76] studied dry CH4 reforming in a microwave-assisted reactor from CO2 utilization/recycling, as shown in Fig. 6. Moreover, COG over an activated carbon catalyst. Such heating mechanism proved dry reforming produces syn-gas with a H2:CO ratio of approxi- superior in CO2 methane reforming compared with conventional mately 2, which is considered ideal for methanol synthesis [16]. methods. Results showed that 100% CH4 and CO2 conversion can During syn-gas production, H2 in the feed COG can cause two be achieved for a long period at an optimum temperature range major problems: (a) a shift in the reaction equilibrium to the reac- of 700–800 °C. Certain thermodynamic factors play an important tants, resulting in low CH4 and CO2 conversion to syn-gas; and (b) role in the COG CH4 conversion to syn-gas via steam, including the induction of the undesired RWGSR. Both effects result in a de- the H2O:CH4 ratio, the conversion temperature, and the reaction crease in H2 content in the final syn-gas, which in turn results in a time. Experimental results have shown that a H2O:CH4 ratio be- low H2:CO ratio, which is unsuitable for methanol synthesis. How- tween 1.1 and 1.3 and a temperature range of 1223–1273 K were ever, results suggested that RWGSR has a more significant effect on optimum for maximum CH4 conversion. A CH4 conversion of the process compared with the shift in the reaction equilibrium. To P95% can be achieved over a H2O:CH4 ratio of 1.2 and at a temper- limit H2 consumption under RWGSR, the reaction should be con- ature of 1223 K [77]. ducted at higher temperatures (P1000 °C) [16]. Maruoka and
Catalytic steam reforming of CH4 is currently the most studied Akiyama [81] proposed a new method for thermal energy recovery and applied process for H2 enrichment and syn-gas production. from hot flue gases generated by the steel-making convertor. The The reaction does not need any gas purification system as in case process includes the use of both latent and endothermic heat from of PO and CO2 reforming. It is also suitable for high pressure appli- the reaction. The stored heat after recovery is supplied to COG to cations and provides easy separation of products. Moreover, steam induce steam reforming of CH4 and obtain syn-gas, which is then reforming can produce syn-gas with high H2/CO ratio, which is utilized for methanol synthesis. Results indicated the process to suitable for the synthesis of different chemicals in many industrial be quite promising for large scale methanol production. processes [70,74,78]. COG steam reforming process occurs through the following main reactions [74]: 3.6. COG tar utilization
CH4 þ H2O $ CO þ 3H2 ð5Þ Hot COG released at a very high temperature (750–850 °C) from coking facilities contains 100 g/m3 tar (benzene, toluene, naph- CH4 þ CO2 $ 2CO þ 2H2 ð6Þ thalene, and sulfide). Tar separation from hot COG not only results in valuable heat loss, but also has serious environmental conse- CO þ H2O $ CO2 þ H2 ð7Þ quences, with the additional challenge of recovering tar from the The product selectivity and final composition may be influenced by stripping liquid. Hot COG tar can be converted into small, lighter some side reactions including dry reforming (6) and WGSR and re- HCs via catalytic hydro-cracking or reforming reactions using the verse water–gas shift reaction (RWGSR) (7). During steam reform- sensible heat and chemical energy of hot COG [82,83]. Ni-based ing, carbon deposition can be successfully addressed by injecting catalysts have been largely investigated for the hydro-cracking of more steam than required stoichiometrically to carry out the complex higher HCs because of their low cost and high activity. reforming reaction (H2O/CH4 >1) [24]. Yang et al. [74] studied However, such catalysts are also prone to sulfur poisoning, carbon steam reforming of COG using NiO/MgO catalyst. A high CH4 con- deposition, and sintering, especially when operated at high reac- version ( 97%) under low steam/carbon (S/C) ratio was achieved tion temperatures, which result in serious catalyst deactivation. at 875 °C with less carbon deposition and enhanced thermal stabil- A key advantage of using hot COG is its 10–15% water content, ity. It was revealed that CH4 and CO2 conversions strongly depend which drives the steam reforming reaction to counter coke forma- upon S/C molar ratio and reaction temperature. Cheng et al. [79] re- tion during COG tar hydro-cracking [82]. Fei et al. [83] used Ni/Ce– ported H2 enrichment through catalytic reforming of hot COG using ZrO2/Al2O3 catalysts with varying Ni-loading and Ce–Zr contents to Ni/Mg(Al)O catalysts. The process can successfully utilize the sensi- study the hydro-cracking of a model tar (toluene, naphthalene) ble heat that may otherwise be wasted resulting in considerable en- from a hot COG. The reaction was conducted at 800 °C under atmo- ergy loss. Results showed that the amount of H2 in the resultant spheric pressure. The catalyst exhibited high activity, long-term mixture increased 4-fold in comparison to the starting mixture with stability, and some sulfur tolerance. The tar constituents were all S/C molar ratio of 1.7. converted into lighter gaseous fuels even at a low steam-to-car- bon-mole ratio (steam: C = 0.44). Coke formation was negligible 3.5. Methanol synthesis over a 7 h operating period, and the catalyst showed excellent per- formance in the direct removal of tar compounds in hot COG and
Methanol is an important chemical feedstock that can be used converting them into useful light HCs. Ni/MgO/Al2O3 catalysts to produce different chemicals, including formaldehyde, methyl [82] also exhibited excellent activity, stability, and carbon resis- tertiary butyl ether, and acetic acid. Methanol is also used as a tance for the catalytic hydro-cracking of tar in hot COG. The results key solvent in many industrial processes, as fuel cells in automo- showed complete conversions of tar compounds into light fuel biles, and for power generation. The production capacity of meth- gases, whereas the presence of H2S in the feed gas actually inhib- anol in China was expected to reach 25 million tons by the end of ited carbon deposition, resulting in an enhanced catalytic activity 2010, with nearly 80% of the production relying on coal-based and long-term stability. Bimetallic catalysts have also been inves- technologies. The global demand for methanol is also expected to tigated for the catalytic reforming of tar compounds from hot R. Razzaq et al. / Fuel 113 (2013) 287–299 295
Fig. 6. Dry CO2 reforming of COG for methanol synthesis [16].
COG. Catalysts promoted the complete conversion of toluene in hot the catalyst both for the reactivity and selectivity. The methanation
COG tar into light CH4, CO, and CO2 gas molecules between 600 and of CO2 is more rapid and more selective compared with that of CO 750 °C at atmospheric pressure. Therefore, a high H2 content and a over Ni, Fe, Rh, and Ru catalysts [90]. Ni is the most studied and low reaction temperature promote CH4 formation [84,85]. considered the most suitable catalyst for methanation of carbon oxides because of its high selectivity for CH4 and its relatively 3.7. COG methanation low price [91–94]. Different support materials have been used for
the dispersion of Ni and other active metals, including SiO2,Al2O3,
The catalytic co-methanation of CO and CO2 (COx) in COG for TiO2, ZrO2, CeO2, and zeolite [95–99]. The activity and selectivity of CH4 enrichment can be regarded as a simple and highly efficient the supported metal catalysts are strongly affected by the amount way of producing gas with high heating value and extensive indus- of metal loading, the size of the dispersed metal particles, the inter- trial and commercial use. COG methanation can occur without the actions between the support and the active species, and the com- addition of other reagents while CH4 can be separated as a valuable position of the support material [100]. Since methanation is an and clean fuel. The reaction has been extensively used in the re- exothermic reaction, the reaction heat results in severe metal sin- moval of carbon oxides from gas mixtures in NH3 plants, as well tering and poor catalytic stability. Therefore, it is imperative to de- as in H2 purification in refineries and ethylene plants [86]. Sabatier velop highly active low temperature methanation catalysts to and Senderens [87] first studied the methanation reaction at the ensure long-term thermal stability and also minimize operating beginning of the 20th century. They found that Ni and other metals costs for large scale industrial applications. Table 4 lists the differ-
(Ru, Rh, Pt, Fe, and Co) catalyze the reaction of CO with H2 to pro- ent catalytic systems used for COx methanation reaction. duce CH4 and water [88]. Many reactions take place during CO and Catalytic CO and CO2 methanation have been mostly performed CO2 hydrogenation, and CH4 is formed as a result of the competi- using a fixed-bed catalytic reactor. However, the use of an efficient tion between such reactions. CO reacts with H2, provided that reactor designed using electrochemical techniques can prove the stoichiometric ratio of the reactants (H2/CO) is at least 3:1, highly cost-effective and environmentally friendly by providing according to Eq. (R-1). However, for a feed gas with a low H2/CO maximum yield with minimal waste production [106]. Bebelis ratio, CO may be hydrogenated via the reaction in Eq. (R-2). CO2 et al. [107] studied the electrochemical CO2 methanation reaction methanation is carried out under a higher H2/CO2 ratio (Eq. (R- over a Rh/YSZ catalyst and concluded that high CH4 production 3)). Undesired WGS reaction occurs in accordance with Eq. (R-4) rates can be achieved as a result of an increase in the Rh catalyst which may significantly affect CH4 selectivity. Another reaction potential (electrophobic property) while operating at a tempera- (Eq. (R-5)) may also occur in case of low H2/CO ratio, resulting in ture range of 346–477 °C. An extensive experimental study on carbon formation and catalyst deactivation [88,89]. the methanation reaction using a fluidized bed reactor operated
0 at 320 °C has also been conducted very recently. For all the exper- CO þ 3H2 $ CH4 þ H2OðgÞ DH289K ¼ 206:2kJ=mol ðR-1Þ iments, a commercially synthesized Ni/Al2O3 catalyst with a large surface area was used. The reactor achieved 100% CO conversion 0 2CO þ 2H2 $ CH4 þ CO2 DH289K ¼ 247:3kJ=mol ðR-2Þ to CH4. The experimental results revealed that the methanation activity inside a fluidized reactor is significantly affected both ther- 0 CO2 þ 4H2 $ CH4 þ 2H2OðgÞ DH289K ¼ 164:9kJ=mol ðR-3Þ modynamically and by the reaction boundary conditions. More- over, an additional benefit of a zero-carbon deposition was also 0 achieved, providing the catalyst with high durability and enhanced CO þ H2O $ CO2 þ H2 DH289K ¼ 41:2kJ=mol ðR-4Þ lifetime [88]. 0 2CO $ C þ CO2 DH289K ¼ 172:54 kJ=mol ðR-5Þ
The methanation reaction for CO and CO2 is usually performed 4. Overview of COG utilization technology between 150 and 400 °C in a catalytic reactor. The choice and prep- aration of the catalyst is the most crucial stage in CH4 synthesis COG processing and utilization will not only boost the energy using COG. Numerous studies have revealed the importance of efficiency of the steel industry but also prevent the emission of 296 R. Razzaq et al. / Fuel 113 (2013) 287–299
Table 4
Comparison between the different catalysts used for COx methanation reported in literature.
Catalyst Preparation method %XCO %XCO2 Highlights Ref.
Ni–Co/CeO2–ZrO2 Co-precipitation 100 95 – Feed gas with similar composition to COG [101]
– High COx conversion
–CH4 selectivity of 99%
Ni/ZrO2 Wet-impregnation 100 100 – Low temperature COx methanation [91]
– Promising system for H2 purification
Co3O4 Precipitation 100 _ – CO methanation in COG [102] – Catalyst active at very low temperature (177 °C) Ni/Zr–Sm Oxidation reduction 100 30 – Complete CO conversion at 200 °C [21] treatment – High conversion attained using a second reactor in series – Long-term stability Ru/carbon Wet-impregnation 100 50 – Complete CO conversion at 340 °C for solo CO methanation – Poor methanation activity for [103]
nanofibers CO/CO2 mixtures – Undesired RWGSR can be inhibited by injecting 30% water (steam)
Ru/Al2O3 Impregnation 100 20 – Complete selective CO methanation at 220 °C [104] – Operating at high gas-hourly-space-velocity
– Very low H2 consumption
Rh/Al2O3 Impregnation 99.9 30 – Higher CO conversion [86]
–CO2 suppression caused by addition of 30% water content
– 99% CH4 selectivity
Ru/TiO2 Wet-impregnation 100 _ – Complete and selective CO methanation at 230 °C [105] – Long-term catalyst stability
Table 5 Technological evaluation of different COG utilization routes.
COG utilization Technology Advantages Disadvantages COG combustion – Direct combustion – Easy on-site implementation – Problems of COG surplus – Steam and electricity – Low operating cost – Need to remove heavy HCs generation – Simple in operation – Combustion inefficiencies DRI production – COG as reducing gas – Easy to industrialize – COG purification and reforming requirements
– Low investment costs – Potential SOx emissions – Lower energy consumption – Greater amounts of off-gas emissions – Enhanced steel quality – Resource issues
– Less CO2 emissions – Early stages of development Hydrogen separation – PSA – Developed both industrially and commercially – Adsorbant recycling issues – Highly energy intensive – Requires purification of heavy and light HCs
– Membrane separation – High purity H2 – Less developed industrially – Consumes less energy – Separation required for heavy HCs – Low capital and operating costs – Simple and Continuous operation – Cryogenic distillation – Commercially available process – High operating costs
– High H2 purity – Needs further development Hydrogen and syn-gas – Partial oxidation – Low Operating costs – Problems associated with pure oxygen supply production – Less energy intensive – Carbon deposition and metal sintering in case of a catalytic system – High energy efficiency – Ideal syn-gas ratio for fine chemical synthesis – Dry reforming – High product selectivity – Energy intensive process
– Potential utilization of GHGs (CO2,CH4) – Low H2/CO ratio
– Low H2/CO ratio suitable for higher HC synthesis – High carbon deposition
– Steam reforming – H2 enrichment – Energy intensive process
– Low carbon deposition – High H2/CO ratio needs adjustment for methanol and/or FTS – Suitable for high pressure applications – Ease of product separation
Methanol synthesis – Partial oxidation – CO2 utilization/recycling – Issues relating H2/CO ratio adjustment
– Dry reforming – Ideal H2/CO ratio for methanol synthesis in case of – Technology under development dry reforming – Steam reforming – Industrially viable process COG tar utilization – Hydro-cracking – Hot COG utilization – Carbon deposition and catalyst deactivation – Tar reforming – Eliminates tar separation process – Technology under development – Recovery of valuable energy (sensible heat and chemical energy) COG methanation – Methane enrichment – Simple in operation – Carbon deposition
– High COx conversion – Metal sintering
– High CH4 selectivity – Technology under development R. Razzaq et al. / Fuel 113 (2013) 287–299 297
harmful green house gases (GHGs) including CO2 and CH4. COG Another running project by Camco-Eurofo in Shanxi Province cap- with high H2 contents carries huge industrial and commercial va- tures waste COG for power generation in a combined cycle power lue considering the future hydrogen economy. At present many plant (CCPP). The unit is expected to generate 864,667 MW h of steel enterprises are trying to minimize their COG surplus while electricity per year, with an annual 849,576 ton CO2 emission utilizing the gas in different on-site process during steel making. reduction [114]. Although extensive research and development has been carried The COG-based methanol production project, one of the largest out to utilize COG surplus, substantial amount of COG is still being of its kind, began production in 2009 in Changzhi City, China. It is a wasted resulting in poor production efficiencies and GHG emis- multi-investor project run by the Tianji Coal Chemical Industry sions. Table 5 provides a summary of different COG utilization pro- Group Co., Ltd. and the Shanxi Lu’an Environmental Energy Devel- cesses with some key advantages and disadvantages. opment Co., Ltd. The project is designed to recover 400 million m3 of raw COG to be converted into 300,000 tons of refined methanol, 11,000 tons of crude benzene, and 10,000 tons of ammonium sul- 5. COG investment and economy fate each year. Both investors poured 1.36 billion CNY into the pro- ject, with expectations of further technological advancements in COG with high energy content not only serves as an important the COG utilization field [115]. Recently, another methanol produc- heat and power source for a coking facility, but is also an important tion plant of the Wuhai Shenhua Energy Company in the Xilaifeng feedstock from which a number of valuable chemicals and byprod- Industrial Zone has been placed in the production line. This COG- ucts can be recovered. to-methanol production unit is based on a new energy-efficient and cost-effective patent technology developed by Sichuan Tianyi 5.1. World scenario Science and Technology. The plant is expected to reduce coal-based methanol production costs by 1100–1200 yuan/ton and gas-based In the past, US iron and steel industry relied heavily on by-prod- methanol by 800–1000 yuan/ton, thereby enabling China to com- ucts such as COG for its electricity production. However, with the pete with the Middle East, which enjoys the lowest cost in natural increase in natural gas supply and reliance on electric arc furnaces, gas-based methanol production in the world [116]. the on-site COG utilization for self-generated electricity has de- For a typical COG plant, the determination of product costs, clined significantly [108]. Almost 40% of the COG produced in the including purified COG, tar, benzene, and sulfate, helps in deter- US is now being utilized as a fuel in BF to replace part of the natural mining the overall efficiency of the process. Cost analysis of COG gas. US Steel Corp. has reported an annual savings of over 6 million in coke plants is conducted on the basis of planned profit levels dollars with a payback period of less than a year while utilizing for commercial purified COG minus the cost associated with the re- COG as BF fuel. The company with a state-of-the art COG process- moval of NH3, aromatic HCs (tar), and H2S from raw gas. On such ing and cleaning facility at Clairton coke plant, processes the COG basis, the raw material (coking coal) should also be considered to until its content is approximately 50–60% H2. Moreover, the sulfur achieve an improved cost distribution between raw materials content of the COG is significantly reduced during the cleaning and products. Hence, the total net cost of individual products processing, allowing it to be used efficiently in the BF [109]. should be distributed with respect to the relative volumes in which COG with a low calorific value can be burnt in specially adapted they are produced [117]. turbines with up to 33% efficiency. Mitsubishi Heavy Industries has successfully developed such turbines which are installed in many steel plants around the world such as Kawasaki Chiba Works (Ja- 6. Concluding remarks pan) and Corus Ijmuiden (Netherland) [110]. In Brazil, the Com- panhia Siderurgica Tubaro (CST) power project based on the The fast economic growth rate of China is pushing its energy Rankine regenerative cycle, utilizes off-gasses such as COG and sector to the limit, with some serious environmental conse- BFG with a total capacity of about 200 MW [22]. A Swedish based quences. As the largest producer and consumer of coke, China re- SSAB Strip Products which is an integrated steel plant is consider- lies heavily on its vast coal reserves to meet its energy demand. ing COG reforming for methanol production. The company esti- The coal chemical industry in China is expected to become an mates that approximately 400 GW h of COG would be available important player in ensuring a sustainable development for a per year for methanol production, yielding approximately green future. 300 GW h of methanol [111]. In Ukraine, The Alchevsk Coke Plant COG is an important and valuable by-product produced during power generating project with waste heat recovery is successfully the coke-making process in the iron and steel industries. China installed to displace the use of natural gas and grid electricity. The annually produces large amounts of COG, but most of the gas is system consists of a highly efficient boiler firing COG and BFG cou- not recovered and used to its potential. COG contains valuable pled with a 9 MW turbine generator with a net annual power gen- combustible constituents, such as CH4 and H2, with a reasonable erating capacity of 54 GW h [112]. heating value. The first step toward COG utilization is its recovery and purification from a coke battery. Hot COG can be used in a BF 5.2. China’s perspective as make-up gas or in heating furnaces within a coking facility. Raw
COG is sent to a treatment plant for NH3,H2S, and tar (BTX) re- Given its high COG throughput, China proves an ideal place for moval. Different by-products obtained during COG purification research and investment in sustainable COG utilization technolo- can be marketed and individually sold. gies. Haldor Topsoe, a Danish-based company, has signed contracts COG after purification is considered suitable for H2, syn-gas, and to build two of the world’s largest COG plants in China to replace methanol production. The large amount of H2 in COG can be effi- natural gas (SNG) plants. The project is under contract with China ciently separated using the PSA technology. Installing a PSA unit
Natural Gas Corporation Limited (CNGCL), operating under the Pet- to recover H2 from COG for onsite use or separate sale is highly rec- ro-China Group. The plant in Wuhai is set to convert waste COG ommended in the steel industry. The high H2 content of COG also into clean and valuable liquefied natural gas (LNG). The production makes COG an ideal feedstock for syn-gas and methanol produc- facility has a capacity of 650 million N m3 of LNG/yr and is ex- tion. The installation of such COG utilization units within a coking pected to be in operation by 2012. The facility will be a model facility can promote the self-sufficiency and environmental friend- for sustainable development for the energy sector in China [113]. liness of the steel industry. 298 R. Razzaq et al. / Fuel 113 (2013) 287–299
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