The fixed-bed batch coal gasification technology should not be applied in a one-size-fits-all manner

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The fixed-bed batch gasification technology should not be applied uniformly. Author/Source: Petrochemical Industry Watch. Date: February 18, 2021. Click-through rate: 38. The fixed-bed batch gasification technology originated in the 1930s; initially, coke was used as the raw material. Over the years, the diameter of gasifiers has continuously increased, and the production scale of single ammonia synthesis lines has also been steadily expanded. By the late 1970s and early 1980s, nitrogen fertilizer enterprises successfully developed a fixed-bed batch gasification process technology using anthracite lumps (or coal briquettes/pebbles) as raw material, which was then promoted nationwide. At its peak, there were over 1,500 nitrogen fertilizer plants of various sizes across all counties in the country; in some counties alone, there were 2 to 3 such plants. It can be said that the fixed-bed batch gasification technology has played a key role in ensuring China’s grain production and fertilizer supply, making significant historical contributions. However, the golden age of fixed-bed batch gasification technology came to an end in the early 1990s. At that time, our country introduced foreign technologies for pressurized gasification of water-coal slurry and dry coal powder, and through continuous improvement and innovation, the technical level was greatly enhanced. Since 2000, and especially in the past 10 years, the market share of advanced coal gasification technologies, including water-coal slurry and dry pulverized coal pressure gasification, has continued to grow. According to statistics from the China Nitrogen Fertilizer Industry Association, by the end of 2019, the domestic production capacity for ammonia synthesis using fixed-bed batch gasification technology with anthracite as raw material was 22.38 million tons per year, accounting for 33.7% of the total national ammonia synthesis capacity ； The ammonia production capacity generated by advanced coal gasification technologies using bituminous coal and lignite as raw materials amounts to 27.18 million tons per year, accounting for 41% of the country’s total production capacity – exceeding for the first time the capacity produced from anthracite coal. The viability of fixed-bed batch gasification plants has been severely constrained, with their share of total capacity dropping from 2/3 to around 1/3. The fixed-bed batch coal gasification ammonia synthesis production technology, which once saw rapid development due to low investment costs, now faces two major challenges in its further development and survival: one is the high price of smokeless lump coal as a raw material ； Second, the amount of unorganized waste gas emissions is high, and the impact of the second issue is particularly severe. In recent years, **given the tightening regulations regarding local safety and environmental protection,** the National Development and Reform Commission included it in the Restricted Category of the \"Guidance Catalogue for Industrial Structure Adjustment (2019 edition)\" ； The “Technical Guidelines for Performance Grading of Key Industries and Formulation of Emission Reduction Measures (Revised Edition 2020)” issued by the Ministry of Ecology and Environment clearly states that enterprises engaged in ammonia synthesis via fixed-bed batch coal gasification are not eligible for Grade A evaluation ； **Departments such as the Emergency Management Department have also issued regulations requiring the restriction and phasing out of this technology. In the first half of 2020, Henan Province and Shandong Province took the lead in introducing policies requiring the phased elimination of the fixed-bed batch gasification process. Relevant departments and experts also recommended phasing out this technology, with some provinces (cities) even implementing blanket policies to that end. This has left the relevant companies confused about their future prospects, resulting in the postponement of upgrades to necessary equipment; some production capacities had to be shut down, leading to significant asset losses and job losses among workers, which in turn affected the workers’ livelihoods and the regional fertilizer supply. So, should the fixed-bed batch gasification technology be phased out or completely replaced? It should be noted that, based on the current capacity of existing facilities, replacing them all with advanced coal gasification technology installations would require an investment of 110 billion yuan. After multiple rounds of elimination, the existing technologies, management practices, and economic benefits of fixed-bed batch coal gasification plants remain at a relatively good level, indicating significant potential for utilization. Especially for those units that have a short operating time, are still largely in good condition, and whose depreciation has not yet been fully reduced to zero – such as units with a capacity of 180,000 tons of synthetic ammonia or 300,000 tons of urea or more – it would be a real shame to apply a one-size-fits-all approach to them! In fact, the waste gas emissions from the fixed-bed batch gasification technology originate mainly from two sources: first, the unorganized waste gas emissions from the gas generation system; semi-water gas enters the scrubber tower where it comes into direct contact with washing water to remove dust and cool down the gas. Harmful substances such as hydrogen sulfide, ammonia, and phenols in the gas phase transfer into the aqueous phase. The washing water then passes through open-type cross-flow sedimentation tanks and cooling towers, during which the harmful substances dissolved in the water are released into the air ； Secondly, hydrogen sulfide present in the gas lift gas, flash vapor, desorption gas, and the carbon dioxide emitted during the desulfurization and decarbonization processes – that is, the waste gases resulting from these processes – can have their hydrogen sulfide content reduced by improving the desulfurization of the converted gas and optimizing the desulfurization process. The concentration of hydrogen sulfide can be kept below 5 milligrams per standard cubic meter, or else the exhaust gases can be collected together and sent to waste heat boilers for combustion. For a long time, the first type of waste gas emissions, namely the unorganized emissions from the gas generation system, have not been effectively addressed. As a key factor determining the success or failure of fixed-bed batch gasification technology, many companies have made it a focus of their technical efforts. Hebei Dongguang Chemical Company was the first enterprise to carry out renovations to its circulating water system for gas production using fixed-bed batch gasification technology. In the second half of 2019, construction of the demonstration project (4 gas generation furnaces) began, and it came online in November of that year ； In November 2020, the renovation of all 42 gas generation furnaces in the plant was completed. The units that were renovated earlier have been in operation for over a year now; they are functioning smoothly, and the actual operational data matches the design specifications. The China Nitrogen Fertilizer Industry Association organized experts to evaluate its technology, giving it full recognition and high praise. The results of operational data monitoring show that the dust concentration at the outlet of the dust removal filter is below 5 milligrams per standard cubic meter, while the temperature of the semi-water gas at the outlet of the scrubber tower is around 25 degrees Celsius; an incremental water injection system is in use. The removal rates of the main pollutants in the wash water after air stripping were 24% for chemical oxygen demand, 99% for sulfides, 12% for total nitrogen, and 23% for volatile phenols. The stripping gas containing harmful components such as hydrogen sulfide and organic substances is sent to the gas generation furnace, while the additional water is stripped in a stripping tower before being sent for treatment at the wastewater treatment facility. The recycled washing water exchanges heat indirectly with the cooling water, thereby preventing waste gas emissions at the source. The coal powder collected during the dust removal process is sent to the waste treatment furnace for combustion, and the wastewater, after treatment, meets the local environmental discharge standards. After the project was implemented, the level of clean production improved significantly. The investment for this renovation is approximately 120 million yuan; after the renovation, the synthetic ammonia production capacity will be 580,000 tons, with an investment of 206.9 yuan per ton of ammonia produced. According to the company’s calculations, the actual cost per ton of ammonia has increased by 31.46 yuan. The renovation of the Dongguang chemical plant is primarily driven by three technologies: the bag-type dry dust removal technology from Shanghai Jingye Company, the circulating water treatment technology from Hebei Yangmei Zhengyuan Chemical Group, and the renovation of gasification furnaces. Through the bag-type dry dust removal technology, the semi-water gas recovered from the waste heat of the waste heat boiler enters a self-cleaning filter (bag), where dry filtration captures over 99% of the coal powder, dust, salts, etc., as well as over 90% of the tar and aerosols present in the semi-water gas. The coal powder and other particles captured by the self-cleaning filter are transported in a sealed manner to the ash bin using a dense-phase pneumatic conveying system via a pump located at the bottom; once collected, they are used as fuel in the waste treatment furnace. In the water treatment technology design, semi-water gas is cooled indirectly in a cooling tower to below 40 degrees Celsius, and then sent to the gas holder through the semi-water gas main pipe. The vapor condensate present in the semi-water gas after cooling in the tower is sent to a stripping tower, where air from the gas generation air blower is used to strip and purify the condensate, thereby removing any trace amounts of flammable components from it. The gas obtained from this stripping process is fed into the gas generation furnace to assist in combustion. The purified condensate is then sent to the wastewater treatment system, where it is discharged in compliance with regulations or reused. The renovation of the gasification furnace includes the automation of the coal feeding system and slag discharge system, as well as improvements to the overall sealing of the furnace. This not only resolves the environmental issues related to gas, water, slag, and dust generated by the furnace, but also addresses the safety problems associated with explosions during coal feeding and burns resulting from slag discharge, thereby enhancing the safety and stability of production operations. Overall, in the renovation of Dongguang Chemical, the organic substances and unburned carbon contained in the pulverized coal captured by the self-cleaning filters are sent to the waste heat recovery boiler for secondary combustion. The conventional equipment used for wastewater sedimentation and separation of coal ash following water washing for dust removal has been eliminated. This has effectively prevented the generation of wastewater, exhaust gases, sludge, and wet residues, thereby achieving zero discharge of waste residues ； The gas generation cooling water is cooled indirectly and undergoes a closed-loop circulation; the additional water generated during the gas generation process is properly transformed and utilized, achieving zero wastewater discharge ； By adopting the intercooling process, the cooling circulating water in the cooling tower does not come into direct contact with semi-water gas, which prevents trace amounts of toxic, harmful, and odorous gases present in the semi-water gas that pass through the self-cleaning filter from entering the cooling circulating water. This solves the problem of waste gas evaporation, and there is no leakage of volatile organic compounds during this process. The air from the gas production furnace was used as the stripping gas, solving the problem of treating stripping waste gas and achieving zero waste gas emissions. Clearly, Dongguang Chemical’s transformation technology is mature and reliable, and it can help the fixed-bed batch gasification technology avoid being phased out. To promote the upgrading of fixed-bed batch gasification technology, the author believes that the following tasks should be carried out: first, to re-evaluate and correctly understand fixed-bed batch gasification technology. To gain a deeper understanding of the technological upgrades in fixed-bed batch gasification, the author presents the following data: In the list of enterprises leading 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 in the ammonia synthesis industry that use fixed-bed batch gasification technology ranked among the top two, with an energy consumption level of 1072–1091 kilograms of standard coal per ton; enterprises that employ advanced gasification technologies ranked from fourth to eighth, with an energy consumption level of 1206–1371 kilograms of standard coal per ton. According to statistics from the China Nitrogen Fertilizer Industry Association in 2019, the average comprehensive energy consumption for fixed-bed batch gasification technology was 1,211 kilograms of standard coal per ton; the energy consumption for water-coal slurry gasification technology was 1,354 kilograms of standard coal per ton, while that for dry powder gasification technology was 1,373 kilograms of standard coal per ton. Most fixed-bed batch gasification technologies are powered by electricity; based on calculations of energy consumption and equivalent conversion factors, the overall energy consumption is 1330–1380 kilograms of standard coal per ton, which is roughly comparable to the overall energy consumption of advanced gasification technologies. Now, let’s talk about the renovation plan for Dongguang Chemical. There is little change in energy consumption; only a slight increase in electricity usage, which is negligible ； In terms of environmental protection, the system is fully sealed to prevent the release of uncontrolled waste gases, thus addressing the issue of waste gas emissions at its source. Although this leads to an increase in wastewater discharge, with an increase of about 1 ton per ton of ammonia produced, the wastewater can still be treated to meet regulatory standards before being discharged ； In terms of safety, both feeding and slag removal in the furnace are automated, eliminating the need for personnel to be on site. This has led to an **improvement in the working environment; the previous messy and unsanitary conditions have been completely eliminated, and the site now resembles those of advanced gasification furnaces ； In terms of competitiveness, given the current situation of Dongguang Chemical, although investments are required for upgrades which in turn increase production costs, these costs remain within acceptable limits. As the domestic capacity for fixed-bed batch gasification continues to decline, the demand for anthracite coal has dropped significantly, and market prices have kept falling. Currently, the price of anthracite coal is about 150–200 yuan/ton lower than that of pulverized coal (previously the difference was 400–500 yuan/ton or even more), **which reduces the cost of producing ammonia. In discussions with companies such as Dongguang Chemical, they believed that, after modifications, the fixed-bed batch gasification technology still has a place in the current market conditions. The greatest advantage of the upgraded technology is reduced equipment depreciation and amortization, lower financial costs, more proficient production operations, and a higher operational rate. Second, **policy or financial support should be provided. **Relevant departments need to change their traditional views on fixed-bed batch gasification technology in the past, and evaluate the modification approaches for this technology in a realistic manner, assessing enterprises based on whether their production facilities meet safety and environmental standards. Clearly, the upgraded fixed-bed batch gasification technology meets all emission standards in every aspect; it should not be classified as a technology subject to restrictions or elimination. It should be allowed to coexist with newer gasification technologies, without adopting a one-size-fits-all approach. Decisions should be based on practical considerations, taking into account the specific needs of each enterprise, plant, and technology. Relevant enterprises should be given a 2–3 year buffer period to urge them to promptly prepare plans, raise funds, and carry out construction work. Furthermore, ammonia production enterprises that currently use fixed-bed batch gasification technology face increasing pressure to meet environmental regulations and a shrinking profit margin for their products, which puts significant strain on them to invest in environmental upgrades. To improve the overall environmental protection standards in the industry, it is necessary to make full use of fiscal and policy funding as a driving force. Enterprises that have advantages such as access to reliable raw material supplies should receive greater support for improving their safety, environmental protection, and quality standards, thereby promoting high-quality development within the industry. Third, enterprises should upgrade their existing production facilities as soon as possible. The situation regarding safety and environmental protection in our country will only become more stringent in the future. If the fixed-bed batch gasification technology is not modified, it will ultimately inevitably be phased out. At present, some companies still have concerns regarding the renovation, such as how to choose a suitable renovation plan, the increase in wastewater volume that may result from the renovation, the impact on current production, the risk of facing a one-size-fits-all approach, and funding issues. In this regard, the author believes that enterprise transformation plans can take Dongguang Chemical as a model for reference; companies with weaker technical capabilities can even directly adopt Dongguang Chemical’s transformation plan, which not only saves time and effort but also reduces risks. If the existing wastewater treatment facilities do not meet the requirements for renovation, it is necessary to carry out expansion and renovation to increase their capacity. The expansion of wastewater treatment facilities mainly involves investment and site issues. Site issues are not a major challenge for companies. In terms of funding, referring to Dongguang Chemical’s renovation plan, the overall investment is not high; if additional financial support from ** is obtained, the difficulties will be further reduced. Furthermore, the renovation process does have a certain impact on a company’s production, but if it is planned properly, the losses can be kept under control. This is especially true for companies that have multiple production units, as rotating the order of renovations can further reduce the impact. It should be noted that a one-size-fits-all approach is a common problem faced by all enterprises using the fixed-bed batch gasification technology. In this regard, the author once again calls for it to be understood that as long as the modified equipment meets local safety and environmental standards, **there is no need for the authorities to shut down the existing equipment. Dongguang Chemical has opened another door for the development of this technology, and there are no engineering or technical risks; it should not be doomed to failure. Of course, enterprises should also keep in mind that for the treatment of wastewater generated from fixed-bed batch gasification, different treatment methods should be adopted based on local environmental protection requirements and water quality standards. At present, the technical bottlenecks in wastewater treatment within the nitrogen fertilizer industry (including coal chemical industries) have been overcome. Treating wastewater with high concentrations of ammonia and phenols generated by fixed-bed coal gasification is no longer a challenging task. Companies such as China National Coal Group Ordos Energy Chemical Co., Ltd. and Shanxi Tianji Coal Chemical Group Co., Ltd. have developed effective treatment methods for such high-concentration wastewater, with some even achieving zero discharge of coal chemical industry wastewater. Fourth, select renovation process technologies based on local conditions. The Dongguang Chemical renovation plan is not the only option. Xinjiang Yihua Chemical Co., Ltd., Guizhou Hongsheng Chemical Co., Ltd., and Gansu Jinchang Chemical Industry Group Co., Ltd. upgraded their gas production units by using atmospheric (pressurized) circulating fluidized bed gasification technology; starting from the end of 2019, these projects were successfully put into operation one after another ； The renovation plans for Shanxi Tianze Coal Chemical Group Co., Ltd. and Shanxi Jinxiang Coal Chemical Co., Ltd. are similar to those of Dongguang Chemical, but the source of the technology is different ； Henan Junhua Chemical Co., Ltd. uses oxygen-enriched oxidation technology ； Hebei Tianyuan Chemical Group Co., Ltd. uses fluidized-bed coal gasification technology that relies on dry coal powder as raw material... Even if funding permits, it is possible to completely demolish and rebuild the facility, adopting advanced coal gasification processes such as water-coal slurry or dry coal powder systems. Fifth, establish a standard system for fixed-bed batch gasification as soon as possible. To date, the \"Emission Standards for Air Pollutants in the Chemical Fertilizer Industry\" have not been officially issued. Requirements for the chemical industry vary across different regions, with standards ranging from high to low; furthermore, the nitrogen fertilizer industry lacks standards for fixed-bed batch gasification after renovation. To adapt to the increasingly stringent safety and environmental protection policies, it is urgent to establish emission standard specifications specifically tailored for the nitrogen fertilizer industry, in order to drive improvements in the industry’s safety and environmental performance. At the same time, as **key industries subject to control during periods of severe air pollution in autumn and winter**, the relevant authorities should treat fixed-bed batch gasification ammonia production enterprises in the same way as advanced gasification enterprises. Those that have completed the necessary upgrades and possess a high level of management should also be rated as Class A enterprises. Sixth is to raise public awareness. Over the course of more than half a century of development in the nitrogen fertilizer industry, significant progress has been made in various aspects, including enterprise management standards, intrinsic safety levels, and pollutant emission levels. However, the public's perception of it remains at an older level; their understanding of the safety and environmental aspects associated with nitrogen fertilizer production is not comprehensive, and there are even certain biases. It is recommended to adopt a promotional approach that combines online and offline methods, with the full participation of enterprises, universities, **, and the general public. This will help society gain a better understanding of fixed-bed batch gasification technology, change the existing perception that this technology is associated with high consumption, large amounts of pollutant emissions, and messy and unsanitary plant conditions. It will also enhance the image and status of nitrogen fertilizer manufacturers, creating a favorable external environment for the development of the nitrogen fertilizer industry and promoting its healthy growth.