"Nature: Chemical Engineering" magazine, a sub-issue of the top international academic journal "Nature" launched in January this year, recently published a paper titled "Tempered Cogeneration: Promoting Reducing Carbon Emissions in Industries Difficult to Reduce Emissions", based on steel and chemical industry The cross-border thinking and convincing data discuss the positive role of Tempered Cogeneration on China's greenhouse gas emission reduction. The article believes that tempering and co-production may become a key strategy to reduce carbon emissions in these two industries, and the realization of China's "double carbon" goal requires more cross-border thinking.
This paper was written by Princeton University in the United States and completed in cooperation with Tsinghua University, Northeastern University's National Key Laboratory of Environmental Protection, Beijing Peking University Pioneer Technology Co., Ltd.(hereinafter referred to as Peking University Pioneer) and other universities, institutes and enterprises. A reporter from China Chemical News recently interviewed the relevant person in charge of Peking University Pioneer, read this article from an industry perspective and "analyzed the doubts."
The picture shows the exterior view of the Shandong Shiheng Special Steel Tempering Coproduction Project constructed by Peking University Pioneer. (Map provided by the company)
Large carbon emitters can expect "negative results in positive" in the production of steel in tandem production
Data shows that in 2020, carbon emissions from the steel and coal chemical industries accounted for 14% and 9% of China's total carbon emissions respectively.
The article pointed out that these carbon emissions are mainly due to the use of fossil energy as raw materials and fuels. The iron reduction reaction in iron-making and the hydrogen production reaction in coal chemical industry are both high-carbon emissions. Using large-scale electric heating to generate high temperatures is not feasible in the short term. In order to reduce carbon emissions, China has taken a series of measures: improving production efficiency, applying green hydrogen, and applying new technologies such as carbon capture, utilization and storage (CCUS). However, the potential to reduce carbon emissions by improving production efficiency is limited, and new technologies such as green hydrogen and CCUS are expected to remain costly through 2040.
Steel gas mainly includes coke oven gas (COG), blast furnace gas (BFG) and converter gas (BOFG). China's steel mills produce about 1.2 trillion standard cubic meters of steel gas every year, mainly composed of carbon monoxide (CO), hydrogen (H2), methane (CH4), carbon dioxide (CO2) and nitrogen (N2). Specifically, coke oven gas has a high concentration of H2(55%-60%), while blast furnace gas and converter gas are rich in CO(23%-27% and 50%-70% respectively). About 50% of this steel gas is consumed as fuel in iron-making and steel-making processes, and the rest is mainly used for on-site power generation. However, the use of steel gas to generate electricity (mainly CO combustion) is high-carbon emissions. The carbon emission factor of CO power generation is 1940 g CO2 equivalent/kWh, which is much higher than that of China's power grid (590 g CO2 equivalent/kWh), and even coal power generation (930 g CO2 equivalent/kWh).
In order to produce H2 in coal chemical plants, coal gasification is first carried out to produce CO, and then a water-gas shift reaction is carried out to produce H2. Statistics for 2020 show that the carbon emissions generated by this process account for about one-third of the total greenhouse gas emissions of China's coal chemical industry.
Tempering and co-production means that steel gas is used to replace coal-based H2 and CO, and is used to produce chemicals after purification and purification. On the one hand, this avoids the utilization method of converting CO into electricity, which is a high-carbon emission factor. On the other hand, it can also save part of the coal consumed in the coal-to-hydrogen production process, thereby significantly reducing greenhouse gas emissions in the steel and coal chemical industries., achieving the effect of "negative negative results positive".
The article believes that tempering and tempering co-production has proven to be completely feasible technically and is expected to become a key strategy to reduce carbon emissions in the two major industries in the foreseeable future.
Steel gas covers demand, saving costs and reducing carbon significantly
By building a model based on industry reality, this paper studies the impact of deploying tempering and co-production nationwide on promoting carbon reduction and reducing corporate costs.
The author developed a geographical database containing 272 steel mills and 187 coal chemical plants across the country (2022 data), and connected existing steel mills and chemical plants with pipelines to spatially quantify the supply of H2 and CO by steel mills, as well as the demand for H2 and CO by coal chemical plants. Then, the author compared independent production and customized an optimization model for tempering and coproduction to match the supply and demand of steel mills and chemical plants on the premise of ensuring better corporate profitability and with the goal of minimizing carbon emissions. The benchmark scheme used is for steel and chemical companies to produce independently, that is, steel plants burn excess steel gas to generate electricity, and coal chemical plants use coal to produce H2 and CO. The comparative scenario adopts a tempering co-production model, that is, H2 and CO are purified from excess steel gas and transported through pipelines to a coal chemical plant for chemical synthesis. Under different carbon prices and pipeline length constraints, the author used life cycle assessments to quantify the greenhouse gas emission reductions and cost reductions of the tempering and coproduction scheme compared to the benchmark scheme.
The research results show that compared with independent production, using coke oven gas to purify H2 for tempering and co-production reduces greenhouse gas emissions by 18.3 tons of CO2 equivalent per ton of H2 produced; using blast furnace gas and converter gas to purify CO for tempering and co-production, greenhouse gas emissions per ton of CO produced are reduced by 1.1 tons and 1.2 tons of CO2 equivalent respectively. Using coke oven gas to purify H2 and replace coal-based H2 can significantly reduce greenhouse gas emissions. In terms of cost, compared with independent production, using blast furnace and converter gas to purify CO and coke oven gas to purify H2 for tempering and co-production, the cost per ton of CO increased by 251 yuan and 134 yuan respectively, and the net cost per ton of H2 decreased by 1278 yuan, the comprehensive cost of tempering and co-production was significantly reduced.
In addition, data shows that longer pipeline connections and higher carbon prices can increase carbon emissions reductions and reduce business costs. When the carbon price reaches 350 yuan/ton (CO2), compared with no carbon tax, carbon emissions can be reduced by 6.9% to 22% and costs can be reduced by 3.4% to 9.8%.
Based on geographical databases of Chinese steel mills and coal chemical plants, the author estimated the plant-level supply of H2 and CO based on blast furnace and oxygen blast furnace (BF-BOF) steelmaking production; also estimated the factory's demand for H2 and CO based on the production of various chemical products (methanol, petroleum, natural gas, olefins, ethylene glycol and ethanol).
The article believes that overall, China's steel mills can provide 3.5 million tons/year of purified H2 from steel gas, equivalent to 19% of the H2 demand of coal chemical plants (18 million tons/year); they can provide 218 million tons/year of CO(85% from BFG and 15% from BOFG), equivalent to 180% of the CO demand of coal chemical industries (121 million tons/year). The steel gas produced by China's steel industry can fully meet the demand for CO in the coal chemical industry, and there is a large amount of surplus.
Enterprise accounting benefits are considerable, and cross-border alliances still need support
It is understood that one of the pioneers of Peking University, one of the authors of this article, has accumulated more than ten years of experience in the field of tempering and cogeneration, and has a deep understanding of relevant technologies and actual industrial development. Li Yankui, head of Peking University Pioneer tempering and co-production business, told reporters that they used relevant research data from the paper to use the technical route of dimethyl ether esterification and hydrogenation process to produce fuel ethanol (DMTE) as an example to evaluate the greenhouse gas emission reduction effect and corporate profitability.
Based on their own business reality, they changed the long-distance pipeline connection in the article to the method of building a new chemical plant near the steel plant. This reduces greenhouse gas emissions from compressed long-distance pipeline gas and also saves the cost of compressed long-distance pipeline gas. The results show that compared with independent production, greenhouse gas emissions per ton of H2 produced were reduced to 18.89 tons of CO2 equivalent, and greenhouse gas emissions per ton of CO produced were reduced to 1.14 tons of CO2 equivalent/1.24 tons of CO2 equivalent (self-blast furnace gas/self-converter gas).
According to chemical balance, the raw material consumption for the production of 1 ton of absolute ethanol is 0.746 tons of methanol, 510 standard cubic meters of CO(equivalent to 0.6375 tons of CO) and 1025 standard cubic meters of H2(equivalent to 0.0915 tons of H2).
If all 9 million tons of newly built fuel ethanol production capacity is calculated based on the use of steel gas, compared with independent production, when tempering and coproduction is adopted, the raw material side cost can be reduced by 288 million yuan/959 million yuan for the fuel ethanol industry.(From blast furnace gas/from converter gas); can reduce greenhouse gas emissions for the fuel ethanol industry by 22.1 million tons/22.67 million tons of CO2 equivalent (from blast furnace gas/from converter gas); a total of 7.734 billion yuan in carbon tax savings for the entire industry/7.935 billion yuan (from blast furnace gas/from converter gas, the carbon price is calculated based on the current 350 yuan/ton).
"It can be seen that the greenhouse gas emission reduction effect achieved by using steel and gas for steel, chemical and co-production is very obvious, and it can also reduce costs, increase profits, and enhance competitiveness for enterprises. Companies benefit, and the environment also benefits." Li Yankui said that tempering and tempering co-production is a win-win strategy.
The reporter learned that my country's gasoline consumption in 2023 will be approximately 149 million tons. Based on this, it can be estimated that the annual demand for fuel ethanol will be 14.9 million tons. At present, the effective fuel ethanol production capacity that has been built is about 5.5 million tons, and there is still a gap of about 9 million tons. Tempering and tempering co-production has proposed a new idea of "solving problems" for this purpose.
At the same time, many industry insiders reminded in interviews with reporters that cross-border alliance and win-win development of steel and chemical companies is not smooth and requires support from all parties. As mentioned in the article, tempering and co-production allows coal chemical plants to significantly reduce costs by saving coal costs and carbon trading benefits; on the contrary, steel plants need to purchase additional grid power when switching steel gas from power generation to chemical production. This significantly increases costs. "In this case, how to balance expenditures and benefits between steel mills and coal chemical plants needs to be considered." Li Yankui said.
In response to this issue, the article also puts forward suggestions: Policy makers can coordinate the income distribution between the two parties and guide the pricing of H2 and CO to encourage the steel industry to adopt tempering co-production; at the same time, provide preferential policy support for companies engaged in tempering co-production will also encourage more companies to participate.
Carbon reduction in industries that are difficult to reduce emissions requires overall thinking and promoting cross-industry coupled development. Promoting cross-border linkage between different industries requires policy support and guidance, so as to achieve the goal of reducing carbon emissions while ensuring the economic interests of enterprises. purpose.
"The 'double carbon' road may as well go in pairs." Li Yankui said.