The Ministry of Industry and Information Technology organized a scientific and technological achievements appraisal on January 20, where China's well-known chemical experts evaluated the "isothermal methanation technology for production of natural gas from coke oven gas" independently developed jointly by Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd., Anhui Huadong Chemical & Medical Engineering Co., Ltd. and Shanghai Hanxing Energy Technology Co., Ltd. The accreditation committee carefully gave audience to the development and technology summary report, test report and user report, as well as the presentation & description of field situation. The experts reached a consensus after inquiry and careful discussion that the Technology, as the world's first technology of its kind, was deemed stable and reliable according to nearly two years of continuous industrial operation, and has reached the international leading level. Hence, this technology was considered compliant with appraisal criteria and recommended to be promoted vigorously in coking industry.
According to JI Zhiyuan, General Manager of Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd., the coke oven gas from coking industry in China is principally used for the production of synthetic ammonia, methanol, power and urban fuel gas etc. Along with the spread of coal-to-synthetic ammonia and -methanol technologies, the reduction in production cost and thermal power generation cost, as well as the replacement of urban fuel gas with natural gas, the comprehensive utilization of coke oven gas is limited, as a result of which coke oven gas is directly emitted at high altitude in some regions, which leads to environmental pollution. In order to enable the cost-effective, low-energy consumption and clean use of coke oven gas, they have since 2009 input a lot of manpower and material resources and developed the one-stage isothermal-bed methanation to produce LNG technology jointly with Anhui Huadong Chemical & Medical Engineering Co., Ltd. and Shanghai Hanxing Energy Technology Co., Ltd. so as to resolve the problems in existing methanation technologies at home and abroad. This technology was applied to the produce LNG from coke oven gas plant of 8,500Nm3/h of Qujing Qilin Gas Energy Co., Ltd. and the produce LNG from coke oven gas plant of 17,000Nm3/h of Otog Banner Jianyuan Coal Coking Co., Ltd. in succession, having achieved long-cycle stable operation.
Industrial operation result showed that the proprietary high-efficiency methanation process of Shanghai Huaxi features short process flow, low cost, small footprint, low energy consumption, simple operation, null need for decarburization process, and high conversion rate of CO (99.95%) etc. JI Zhiyuan told the reporter of China Chemical Industry News that this technology exhibits high tolerance, strong adaptability, and high conversion rate for CO and CO2 in coke oven gas (carbon monoxide conversion rate ≥99.95%; carbon dioxide conversion rate ≥99.9%; CO+CO2 at reactor outlet <50ppm), and could be connected directly with cool box without the need for decarburization process. The quality of LNG product is superior to national standards: Total hydrocarbon content is more than 99%; methane content is more than 97%; gross calorific value is 37.57 MJ/Kg; CO2 content <100ppm; content of hydrogen sulfide is 0. The coke oven gas/LNG ratio is high (2.6:1).
It is described that this technology has the following innovative points as compared with domestic and foreign multi-stage adiabatic methanation technologies: First, coke oven gas methanation reaction is completed by one pass without the need for circulating compressor and water vapor supplement. Second, the pressure of methanation reaction system is less than 1.5MPa, and the overall energy consumption of plant is reduced by 15-20%. Third, the operating temperature of methanation catalyst is below 300°C, which contributes to a long service life. Fourth, the short technological process saves 70% of investment, and is easy to control and operate.
Taking a 1,000,000 t/a coking plant where the by-product coke oven gas output is approx. 25,000m3n/h for example, the production of LNG with the one-stage adiabatic methanation technology of Huaxi could save about RMB 20,000,000 Yuan of project investment; the overseas proprietary technology fee of approx. RMB 15 million Yuan could be saved; 200kWh of power could be saved -- a total of RMB 1.5 million Yuan could be saved per year.
According to JI Zhiyuan, this technology offers a high-benefit and high-efficiency utilization method for coke oven gas, thus enabling perfect economic and social benefits for improvement in the efficiency of comprehensive utilization of coke oven gas. In addition, this technology has extensive application in coal-to-synthesis gas, coal-to-natural gas, and carbon monoxide conversion etc. in petrochemical industry, coal chemical industry and fine chemical industry, thus of extremely vital significance for the alleviation of natural gas shortage, clean chemical production, smog pollution control, and integrated utilization.
Make efficient use of coke oven gas based on technology innovation
HUANG Jingan, former Chairman of China Coking Industry Association
China is the world's only coke producer and seller where the coke production is more than 100 million tons. The coke and semicoke production reached 476.91 million tons in China in 2014, accounting for nearly 70% of the global coke production; in addition to the extremely low volume exported, over 98% of the coke was used for domestic consumption. A lot of coke oven gas and blast furnace gas is produced during the production and consumption of coke; the part produced in coking process is for internal use, and approx. 90 billion cubic meters of coke oven gas and a lot of blast furnace gas is left over; the latter was usually used for billet heating in steel works, power generation or methanol production etc. in the past, so the added value is relatively low; moreover, there were no appropriate advanced technologies to be introduced or borrowed from foreign countries. With the technical progress and innovation in coking industry, as well as the increasing urgency for development and utilization of clean energy and the value and benefit improvement of coking companies, a number of coking technology companies and coking enterprises have developed innovative technologies for production of natural gas from coke oven gas or the mixture of blast furnace gas there-with in recent years. 13 technology companies developed a total of 15 projects in different sizes with different features during the period from 2009 to the end of 2014, the handling capacity of coke oven gas for production and pilot production plants was about 4.6 billion cubic meters.
The isothermal methanation reaction-based technology for production of natural gas from coke oven gas developed by Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd. has been subjected to nearly two years of continuous operation in Qujing, Yunnan Province and Inner Mongolia Jianyuan Coking. With this advanced technology, coke oven gas methanation plant works on a "one-pass" basis without the need for circulating compressor and water vapor supplement; the pressure of methanation reaction system is less than 15MPa, which contributes to low energy consumption; the operating temperature of methanation catalyst is below 300°C, thus enabling a long service life; this technology exhibits obvious advantages and characteristics like short technological process, low investment cost, simple control, easy operation, high stability and reliability, high ratio of producing LNG from coke oven gas and outstanding economic and social benefits etc., and its developer has been rated as an industry demonstration enterprise.
The Chinese economy is evolving towards more advanced form, more complex division of labor, and more rational structure; the economic development gets into a new normal state, shifting from high growth rate to medium-and-high growth rate; the economic development is changing from scale and speed-oriented extensive growth to quality and efficiency-oriented intensive growth; the economic structure is changing from the focus on incremental expansion to in-depth adjustment featured by stock regulation and growth optimization; the economic development is shifting from traditional growth points to new growth points. In this context, the coking industry in China gets into a new normal state of growth rate adjustment, where the "synergistic effect" of the elimination of serious excess production capacity, the survival of the fittest businesses, the environmental regulations' restrictions and the transformation & development acceleration has pushed a good few businesses into a severe test of meager profit or loss. We are looking forward to the mushrooming, improvement & perfection, and increasingly active effect of advanced technologies like the isothermal methanation reaction-based coke oven gas-to-natural gas technology of Shanghai Huaxi Chemical. It's more advisable to intensify the technological innovation and green transformation, give play to the integration of more advanced applicable technologies, and strive to stimulate the rational high-efficiency sustainable development of coking industry.
Isothermal methanation-based coke oven gas-to-LNG process is composed of coke oven gas purification, one-stage isothermal methanation and cryogenic process etc.:
Coke oven gas purification technology: Coke oven gas purification consists of rough desulfurization, TSA, PSA pretreatment and fine desulfurization.
The rough desulfurization of coke oven gas is realized with HX-Z series of solid desulfurizing agent developed by Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd. This desulphurizing agent has extremely high desulfurization activity and sulfur capacity.
The pressure of desulfurized coke oven gas is reduced to 0.3MPa (G) with a compressor and delivered to TSA pretreatment unit from the bottom; two units are in the state of adsorption removal of oil, naphthalene and benzene, while one unit is in a state of regeneration. The gas pretreated in TSA is delivered to PSA pretreatment unit, where the residual impurities in feed gas are removed to obtain purified coal gas. With respect to the units of PSA pretreatment column, two are for adsorption, and one for regeneration. The pretreated coke oven gas is desulfurized through Co-Mo hydrogenation and zinc oxide to reduce the total sulfur concentration in coke oven gas to less than 0.1ppm before the delivery to methanation segment.
One-stage isothermal methanation technology: This technology employs the special one-stage isothermal tube-array methanation reactor developed by Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd. Methanation catalyst is located at tube side, and the water is at shell side. The reaction heat is transferred in a timely manner through boiling heat absorption of high pressure water during reaction so as to keep constant temperature at the outlet of methanation reaction. Process gas passes through methanation reactor on a single-pass basis without the need for circulating gas and vapor supplement, and this helps to reduce energy consumption and save 70% of investment cost.
Since the isothermal tube-array reactor enables methanation at low temperature, the conversion rate of CO is ≥99.95%, while the CO2 conversion rate is ≥99.9%. Moreover, this reactor assures the long service life of catalyst by avoiding excessively high hot-spot temperature of catalyst.
The one-stage isothermal methanation technology transfers reaction heat in a timely manner to maintain low bed temperature (260-280°C). The production at relatively low pressure helps to reduce energy consumption of coke oven gas compression and extend the service life of catalyst. The merits of this technology include short process, zero power consumption, low investment, and long service life of catalyst.
Natural gas liquefaction technology: National gas refrigeration/liquefaction process could generally be divided into three categories, i.e. cascade (step) cycle process, expander refrigeration process, and mixed refrigerant refrigeration process. This plant is furnished with advanced mixed refrigerant cycle (MRC) with gas pre-cooling.
Application of isothermal methanation for producing LNG from coke oven gas:
WEN Shangjun, the Chief Engineer of Otog Banner Jianyuan Coal Coking Co., Ltd.
Otog Banner Jianyuan Coal Coking Co., Ltd., as a large coal chemical enterprise specializing in coal mining, washing, dressing, coking and chemical engineering, began to survey and study the project of producing LNG from coke oven gas in April 2011 following the principle of "environmentally-friendliness and cyclic development", and decided to employ the isothermal methanation process independently developed by Shanghai Huaxi Chemical Industry Science & Technology Co., Ltd. after the repeated investigation of advantages and disadvantages in the projects of producing LNG from coke oven gas at home and abroad. The design of this project was started in October 2011; the civil construction was commenced in April 2012; the project was brought into service and produced acceptable LNG product in October 2013. The feed gas handling capacity is 17,000Nm3/h, and the production capacity is 6,000Nm3/h. During the plant operation of over one year, the CO output was basically 0 at methanation reactor outlet; the CO2 concentration was less than 10ppm; the content of C2H6 and higher components was less than 1.2%; the CO and CO2 conversion rates were superior to the design value. The practical production of more than one year showed that isothermal methanation process is feasible and worthy of promotion thanks to the high conversion rates of CO and CO2, the simple and stable operation, the low investment cost, the null need for circulation and vapor supplement, and low energy consumption.