Intermittent gasification technology should be re-evaluated

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Re-evaluating intermittent gasification technology Author/Source: China Nitrogen Fertilizer Industry Association Date: 2021-01-07 Clicks: 10 The capacity for ammonia production through atmospheric-pressure fixed-bed intermittent gasification has played a significant role in ensuring the supply of fertilizers. However, as environmental regulations become increasingly strict, and with wave after wave of phasing-out measures, many entrepreneurs wonder whether intermittent gasification technology is still suitable for the development of the coal chemical industry How much longer can enterprises survive after switching from direct cooling to indirect cooling? Oxygen-enriched gasification requires huge investment, and a full-process replacement with new types of gasification involves even more enormous costs – so what is the way forward? The emergence of the fixed-bed environmental protection improvement model in Dongguang Chemical Industry in Hebei has brought hope to companies facing difficult decisions, as well as hope for the entire industry. Industry experts believe that intermittent gasification technology, which can meet requirements such as safe and controllable operation as well as environmental and quality standards through upgrades and modifications, should not be classified as a technology to be restricted or phased out. This technology should be treated with a scientific approach, and it is necessary to reevaluate and properly understand it. The production capacity of intermittent gasification declined sharply. In the 1960s, to address the critical constraints in China’s food and fertilizer industries, small nitrogen fertilizer plants that used smokeless lump coal as raw material and employed intermittent gasification technology were established. Over the following decades, China’s nitrogen fertilizer industry developed gradually, starting from nothing and growing from small scale to larger one, continuously expanding and strengthening. By 2010, coal-based ammonia/sulfuric acid fertilizer production via intermittent gasification had become dominant in the industry, accounting for 68% of total production, and played a crucial role in ensuring food security. Subsequently, influenced by the rapid development of new gasification technologies that use low-cost bituminous coal as raw material outside the anthracite-producing areas, the dominant position of the batch gasification process gradually declined, and the capacity for producing synthetic ammonia decreased; in 2019, this capacity was 22.38 million tons, accounting for 33.7% of the total annual production capacity. Production capacity has been reduced by more than half over the past 10 years; the reasons for this are mainly economic considerations as well as environmental and safety issues. The price per tonne of anthracite and Shenmu coal can differ by up to 400–500 yuan at times; this serves as an important driving force for companies that adopt new coal gasification technologies. It is also the main factor behind the changing proportions between traditional coal chemical processes (intermittent coal gasification) and new ones, and it represents an inevitable outcome of historical development. While various new coal gasification technologies are developing rapidly and competing fiercely, there is an ever-increasing outcry that batch coal gasification is “environmentally unfriendly” and “unsafe.” There seems to be a strong determination to eliminate this “black sheep” that is deemed “outdated,” “unsafe,” “environmentally harmful,” and “uneconomical.” But is that really the case? The energy consumption for emissions is similar to that of modern gasification processes. Over the years, the automation level and environmental safety aspects of intermittent gasification processes have continued to improve. These processes offer advantages such as mature technology, reliability, lower investment costs, reduced overall energy consumption, low operational and maintenance expenses, and low financial costs. However, they also have disadvantages, including high raw material prices and the need for further improvements in environmental protection standards. In terms of environmental protection, there are drawbacks such as uncontrolled emission of waste gases from the gas generation circulating water system, emission of sulfur-containing waste gases during desulfurization and decarburization processes, and a high carbon content in the waste residues. However, the pollutant emission levels and energy consumption at other sites are comparable to those of modern coal gasification. Wastewater discharge: The amount of wastewater discharged (based on the total outlet) is approximately 2–3 cubic meters per ton of ammonia, meeting the national special emission standards requiring ammonia nitrogen levels to be below 15 milligrams per liter and COD levels to be below 50 milligrams per liter. The wastewater discharge from the 11 fixed-bed batch gasification plants in Jincheng, Shanxi Province, is subject to the strictest standards corresponding to Class III and Class V water environment functional zones for surface water: ammonia nitrogen levels must be below 1.5 mg/L and 2.0 mg/L respectively, while COD levels must be below 30 mg/L and 40 mg/L respectively. Regarding exhaust gas emissions, the flue gases generated by systems with a ventilation capacity of 65 tons per hour or less, as well as those from waste gas incineration units, are all subjected to environmental protection upgrades such as desulfurization, denitrification, and dust removal. After these treatments, they are required to meet the emission standards applicable to coal-fired boilers of similar scale. These standards comply with the \"Emission Standards for Air Pollutants from Boilers\" (DB14/1929-2019) implemented in Shanxi starting from May 1, 2020; the allowable levels are no more than 20 milligrams per cubic meter for particulate matter, 100 milligrams per cubic meter for sulfur dioxide, and 150 milligrams per cubic meter for nitrogen oxides. Some enterprises that use mixed waste combustion furnaces have achieved ultra-low emissions. The flue gas recovery device for intermittent gasification boilers; secondly, the gas generation circulating water system generates a large amount of unorganized waste gas emissions. At present, most enterprises in the Beijing-Tianjin-Hebei region use trench sealing, sedimentation tank sealing, and exhaust gas collection, with the gases being sent to gas furnaces or boilers via gas generation blowers or boiler blowers for combustion. Hebei Dongguang Chemical has transformed the direct spray cooling method used for gas generation into an indirect cooling method, thereby addressing the issues of uncontrolled exhaust gas emissions as well as the unpleasant odors resulting from the drying of coal sludge. Thirdly, the desulfurization and decarbonization processes in downstream units generate unorganized waste gases. Enterprises in the Beijing-Tianjin-Hebei region have begun to collect these gases collectively and send them to boilers or waste treatment furnaces for thermal combustion, or to use washing and adsorption methods for treatment, in compliance with local environmental protection regulations; enterprises in Jincheng City, Shanxi Province, have already completed such treatment. Waste discharge: The slag generated in the intermittent gasification process amounts to about 230 kilograms per ton of ammonia produced. The carbon content in this gasification slag ranges from 13% to 18%. Due to its high carbon content, it is usually sent to boilers or waste incineration plants for mixed combustion, after which the carbon content drops below 3%. The amount of slag produced in new coal chemical processes is approximately 120–240 kilograms per ton of ammonia, and the carbon content in the gas generation slag is less than 3%. In comparison, the emission levels of the two are similar. In terms of energy consumption, in the list of companies that led in energy efficiency among key energy-consuming industries for the year 2020, published by the Ministry of Industry and Information Technology in December 2020, enterprises using intermittent gasification processes in the ammonia synthesis industry ranked among the top two, with an energy consumption level of 1072–1091 kilograms of standard coal per ton ； Companies using bituminous coal/lignite as raw materials in new coal gasification processes rank from fourth to eighth, with an energy consumption level of 1206–1371 kg of standard coal per ton. According to statistics from the China Nitrogen Fertilizer Industry Association in 2019, the average comprehensive energy consumption for the intermittent gasification process was 1,211 kilograms of standard coal per ton, while it was 1,354 kilograms of standard coal per ton for the new gasification process. Most intermittent gasification processes are powered by electricity; when calculated based on energy consumption, their overall energy consumption ranges from 1330 to 1380 kilograms of standard coal per ton, which is comparable to the overall energy consumption of new gasification processes. There are problems; on one hand, it is the issue of uncontrolled discharge of circulating water. Compared with the emissions of \"three wastes\" in new coal chemical processes, the environmental issue associated with the batch gasification process is the waste gases emitted from the gas generation circulating water. On the other hand, there is the issue of a lack of technologies for controlling unorganized emissions. Dust, water-soluble gases, sulfides, aerosols, as well as organic substances such as phenols and tar in gas enter the gas generation circulating water system through washing, resulting in a complex composition of the water quality and making wastewater treatment very difficult ； The emission of VOCs from circulating water poses an environmental challenge for enterprises, as there are no mature technical solutions available in China for addressing this issue at the end-of-pipe stage. Intermittent gasification blowing air recovery devices: Strained policies present tough choices for enterprises. In recent years, as environmental protection policies have become increasingly stringent, various measures such as policies for phasing out polluting technologies, environmental management policies, and emergency emission reduction measures have been introduced. As a result, enterprises are faced with the decision of either upgrading their gasification processes at the source or carrying out environmental upgrades to those processes. The first is the environmental protection \"phasing-out\" policy. The \"Action Plan for Comprehensive Control of Air Pollution in the Beijing-Tianjin-Hebei Region and Surrounding Areas during the Autumn and Winter Seasons 2019–2020\", the \"Action Plan for Comprehensive Control of Air Pollution in the Beijing-Tianjin-Hebei Region and Surrounding Areas sowie the Fenwei Plain during the Autumn and Winter Seasons 2020–2021\", Shanxi Province’s \"Action Plan for Protecting the Blue Sky in 2019\", and Shanxi Province’s \"Implementation Plan for Comprehensive Control of Air Pollution from Industrial Furnaces\" all call for the phasing out of a certain number of fixed-bed batch gasification units used in the fertilizer industry; the enterprises to be phased out are mainly those that are old and lack sufficient safety and hygiene distances. The Ministry of Ecology and Environment has never proposed a one-size-fits-all policy for phasing out fixed-bed batch gasification units. The second is environmental protection and governance policies. In 2019, the Ministry of Ecology and Environment issued the \"Comprehensive Plan for Controlling Air Pollution from Industrial Furnaces,\" which stipulates that in industries such as nitrogen fertilizer production, where fixed-bed batch gasification furnaces are used, efforts should be accelerated to replace direct water cooling with indirect cooling for gas cooling. Third are emergency emission reduction policies. The 2020 letter issued by the Ministry of Ecology and Environment titled \"Notice on Issuing the Technical Guidelines for Formulating Emergency Emission Reduction Measures for Key Industries during Severe Pollution Weather (2020 Revised Edition)\」stipulates that the fixed-bed batch gasification process does not meet the standards for Class A enterprises; failure to address the emissions from cooling towers or to carry out 30% renovation of the gasifiers means that such facilities cannot meet the standards for Class B enterprises, while Class C enterprises are required to reduce their production by 30%. Fourth, Shandong Province has introduced a policy stating that by 2022, all fixed-bed gasification furnaces used in urea production facilities must be phased out, while Henan Province has set a target to eliminate fixed-bed batch gasification furnaces in the chemical industry by 2020. These policies have made companies even more skeptical and pessimistic about the prospects of this industry. In summary, implementing environmental protection technological upgrades for intermittent gasification processes is an important task that enterprises must undertake. However, the difficulties in making such decisions lie in the fact that replacing the entire gasification process involves huge investment, a long construction period, as well as strict constraints related to land procedures and park planning. Secondly, converting the gasifier to pure-oxygen continuous gasification requires significant investment and occupies a large area; there is no specific policy support, and its operational duration is uncertain. Third, the investment required for indirect cooling upgrades is relatively low, but specialized wastewater treatment facilities are needed; there is no specific policy support, the duration of such systems’ operation is uncertain, and they may also face the risk of being phased out after the upgrades are completed. Taking the case of a plant with an annual production capacity of 600,000 tons of ammonia and the retrofitting of 40 batch coal gasifiers as an example, the cost of implementing indirect cooling modification is 150 million yuan; switching to pure oxygen-based gas generation requires 800 million yuan; while replacing the entire process with a new coal gasification technology utilizing coal water slurry (or dry powder) necessitates an investment of 3 billion yuan. The small and medium-sized nitrogen fertilizer industries and enterprises have long operated with meager profits to support agriculture, remaining in a state of weak balance with limited resources; they have always operated at a level sufficient only for basic needs. Coupled with the staggered production schedules in recent years, it has become extremely difficult for these enterprises to survive. Alternative upgrading technologies bring hope; intermittent gasification urgently needs an environmentally friendly upgrading solution for transition gasification. From 2019 to 2020, Hebei Dongguang Chemical focused on the core issues related to environmental protection in the industry and pursued bold innovation. The fixed-bed environmental protection improvement model developed by them has great practical significance. It provides a solution for ensuring environmental compliance in traditional batch gasification processes. Moreover, it offers both technical and temporal support for phasing out the batch coal gasification process and transitioning to a new type of anthracite lump coal gasification technology, thereby contributing to the economic development of the lump coal industry. By applying this model, the direct cooling of gas generation cooling water was replaced with an indirect cooling system in a closed cycle along with proper purification processes, thereby achieving \"zero emissions\" of waste gases and wet residues” ； The incremental wastewater can be discharged directly or reused after being treated at the wastewater treatment plant ； It addresses environmental issues such as the difficulty in treating phenol-cyanide-containing wastewater generated in gas production, strong odors, and VOC emissions. From November 9 to 10, 2020, in Cangzhou, Hebei, relevant leaders and experts from organizations such as the China Nitrogen Fertilizer Industry Association, the Raw Materials Industry Department of the Ministry of Industry and Information Technology, and the Chinese Academy of Environmental Sciences gathered to discuss ways to improve the environmental performance of intermittent gasification technology. The China Nitrogen Fertilizer Industry Association organized experts to conduct an evaluation of the technological achievements related to the treatment of volatile pollutants in the circulating water used in the fixed-bed batch gas generation process at Hebei Dongguang Chemical. The expert group stated that this technology possesses independent intellectual property rights, the device operates stably and reliably, and it is at the leading level in China; they agreed to approve the evaluation of these achievements. The expert group also noted that this technology achieves zero emissions of wet slag and VOCs in fixed-bed batch gasification processes, as well as ultra-low emissions of wastewater, thereby setting a model project and transformation approach for improving environmental standards in fixed-bed systems across the entire industry. In addition, commissioned by the Ministry of Industry and Information Technology, the China Fertilizer Industry Association is conducting a study on \"Environmental improvement approaches for fixed-bed gasification technology.\" Research indicates that under stringent policy pressures, the production capacity of fixed-bed atmospheric-pressure batch coal gasification following an upgrade in environmental protection standards will reach a level comparable to that of new coal gasification technologies; likewise, its pollutant emission levels will be similar to those of such new technologies. Through analysis and research, the development potential of fixed-bed coal gasification-based ammonia production enterprises is mainly reflected in the following aspects: First, there is a significant improvement in the level of automation. Second, the overall energy consumption of advanced enterprises utilizing atmospheric-pressure batch coal gasification is comparable to that of new coal gasification technologies. Third, environmental performance sees a substantial improvement following upgrades and renovations. Fourth, this technology aligns with the characteristics of China’s energy structure. Fifth, it helps ensure the safety of fertilizer use and increases farmers’ incomes. The successful and stable operation of the Dongguang Chemical Demonstration Plant in Hebei has provided a strong boost to the sustainable development of the fixed-bed, atmospheric-pressure, batch gasification ammonia synthesis technology. The effective resolution of the issue of uncontrolled emissions of waste gas from the cooling water used in gas production has significantly enhanced the competitiveness of this technology. The implementation of upgrading and renovation projects is the result of continuous technological innovation and progress within the industry. Fixed-bed gasification technology, which meets various emission standards, should not be classified as a technology that needs to be restricted or phased out; rather, this technology should be viewed from the perspective of scientific development, allowing different gasification technologies to coexist and ensuring a truly diverse landscape of leading gasification technologies. Treatment device for fugitive emissions from the gas-making circulating water tank in intermittent coal gasification plants. Currently, new enterprises use advanced gasification technologies, while pure oxygen gasification is more suitable for methanol production; enterprises using traditional batch gasification technologies are suited for environmental upgrades. Chemical enterprises must recognize the new situation, adapt to the new normal, and accelerate their pace of transformation and upgrading. Intermittent gasification plants should implement environmental protection measures as soon as possible, particularly to address the issue of uncontrolled waste gas emissions from the gas generation system at the earliest opportunity. Traditional industries are not synonymous with backward industries. As long as they can be utilized and meet environmental protection requirements, transformation and upgrading is the only way forward. The shortcomings of intermittent gasification do not stem from problems with the gasifiers themselves; rather, it is necessary to address the issue of emissions. We must shift from the mindset of “it’s essential to modify gasification processes” to one where “environmental governance and upgrading are indispensable.” “Since the 13th Five-Year Plan period, each individual intermittent coal gasification enterprise has invested over 100 million yuan in measures such as ultra-low emissions control for boiler flue gases, management of fugitive particulate matter, treatment of exhaust gases recovered from gas production and blowdown processes, control of VOCs, and mitigation of unpleasant odors. As a result, the overall environmental quality in the region has seen significant improvement. In the second half of 2020, a total of 9 enterprises in Jincheng City, Shanxi Province, and 1 enterprise in Jinan, Shandong Province, were carrying out indirect cooling retrofits. In addition, enterprises in the Jincheng area will continue in 2021 to carry out projects such as the construction of wastewater treatment plants as part of indirect cooling upgrades, ultra-low emission upgrades for waste heat boilers and blast furnaces with a capacity of less than 65 tons, advanced treatment of flue gases to remove sulfur and carbon, and the comprehensive utilization of gas generation furnace slag. ““Obsolete” technologies must be re-evaluated. Gu Zongqin, Chairman of the China Nitrogen Industry Association, conducted research in coal chemical enterprises in Jincheng City regarding the environmental protection and upgrading of nitrogen fertilizer production via fixed-bed intermittent gasification. The China Nitrogen Industry Association stated that after decades of development, the fixed-bed atmospheric-pressure intermittent gasification technology is no longer considered an outdated, small-scale production method characterized by high pollutant emissions. The level of automation in production facilities has significantly improved; following such upgrades, the emissions levels and the comprehensive utilization of energy and resources now meet current requirements for green development. Therefore, one should not judge a technology’s level based solely on its name. Instead, policies and market competition should be utilized to gradually phase out such production capacities. The industry should identify the key issues, take into account local conditions and the specific characteristics of each enterprise, and develop environmental improvement pathways suitable for different companies. This is also the most effective way to pursue sustainable development at a time when the nitrogen fertilizer industry is facing multiple pressures and operating under heavy constraints. At present, the nitrogen fertilizer industry lacks fully applicable standards, and the \"Emission Standards for Air Pollutants in the Chemical Fertilizer Industry\" have not yet been issued. In light of the increasingly stringent requirements imposed by industrial policies, it is urgent to establish emission standards specific to the nitrogen fertilizer industry (fixed-bed atmospheric pressure batch gasification) in order to regulate and drive continuous improvements in the industry’s environmental protection standards. Fixed-bed gasification nitrogen fertilizer companies are under increasing policy pressure. As an industry that supports agriculture, nitrogen fertilizer products have limited profit margins, and investing large amounts of capital in environmental upgrades poses a significant burden on small and medium-sized enterprises. Therefore, to improve the overall environmental protection standards in this industry, it is necessary to make full use of financial resources and policy incentives. Enterprises that have an advantage in terms of raw material supply should receive greater support in improving environmental protection standards and upgrading their raw material structures, so as to promote the high-quality development of the industry in a orderly and sustainable manner. As a pillar industry of agriculture, after more than half a century of development, the nitrogen fertilizer industry has made significant progress in corporate management, intrinsic safety, and pollutant emissions. The China Nitrogen Fertilizer Industry Association recommends adopting various promotional methods to help the public gain a better understanding of coal chemical technology, thereby breaking the entrenched perception that fixed-bed gasification nitrogen fertilizer plants are energy-intensive, produce large amounts of pollutants, and have messy and unsanitary facilities, and to enable the public to reassess fixed-bed gasification technology.