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Prospects for the clean utilization of high-sulfur petroleum coke. Song Xingxing. Petroleum coke is a product of the delayed coking units in refineries; it features a high calorific value, low ash content, relatively high levels of nitrogen and sulfur, high moisture content, and low volatility. Its production volume accounts for approximately 25% to 30% of the crude oil used as coking feedstock. Before the 1990s, China’s refining industry primarily processed Daqing crude oil with low sulfur content. During this period, the petroleum coke produced by domestic refineries had excellent industrial application properties, and could replace coke in the production of high-quality steel. Established in 1971, Wuhan XX Chemical Plant of Sinopec Group originated as a petroleum coke refining workshop under the large-scale Wuhan Iron and Steel Company. Acicular coke produced from low-sulfur petroleum coke after further processing is a high-quality raw material for manufacturing electrodes, and it is widely used in industries such as electrolytic aluminum and electrolytic copper. As China’s refining industry processes an increasing amount of imported high-sulfur crude oil from the Middle East, the properties of petroleum coke have changed significantly. These changes are characterized by high levels of sulfur (4 wt%) and heavy metals; using such petroleum coke in the steel industry reduces the quality of the steel produced, while its use in the aluminum electrolysis industry lowers production efficiency. In summary, high-sulfur petroleum coke is not suitable as a raw material for the chemical and metallurgical industries with high requirements, which **reduces its value**. So what are the prospects for using high-sulfur petroleum coke as fuel in industrial boilers? In terms of volatile matter content, high-sulfur petroleum coke is similar to anthracite. With existing combustion technologies, it is not difficult to achieve stable combustion of high-sulfur petroleum coke; the challenge lies in the fact that its combustion produces large amounts of sulfur dioxide, causing severe air pollution. Although the calorific value of high-sulfur petroleum coke is 1.5 to 2 times that of coal, due to the above two reasons, its market price can only reach 1/3 to 1/4 of the coal price. How to achieve the clean utilization of high-sulfur petroleum coke and improve economic efficiency has become an issue of concern for the domestic refining industry. Some refineries that began large-scale processing of imported high-sulfur crude oil earlier have started experimenting with mixing petroleum coke into coal-fired boilers. Sinopec Guangzhou XX Plant and Tianjin Shix Company use petroleum coke as a supplementary fuel in the coal powder boilers of their own power plants. Using petroleum coke in coal-fired boilers can bring significant economic benefits, but due to its low volatility, it is difficult for the mixture of coal and petroleum coke to ignite and burn completely, which affects the stable combustion of the coal-fired boiler. Furthermore, as the proportion of petroleum coke used in combustion increases, the thermal efficiency of the boiler is affected, and the sulfur dioxide content in the flue gases rises significantly. Existing coal-fired boilers do not have flue gas desulfurization devices, which can lead to low-temperature corrosion and environmental pollution. It seems that the simple co-firing process is merely a temporary solution and not suitable for widespread adoption. The circulating fluidized bed boiler (CFB) combustion technology is a highly efficient and low-pollution clean combustion technology that has seen rapid development in recent years. Its main features lie in the multiple cycles of the fuel and the desulfurization agent limestone, which enables repeated low-temperature combustion and desulfurization reactions. This approach not only results in low NOX emissions, a 90% desulfurization efficiency, and a combustion efficiency comparable to that of coal powder boilers, but it also offers advantages such as wide fuel adaptability and good load regulation performance. Currently, there are two methods for burning high-sulfur petroleum coke in circulating fluidized bed boilers: mixed combustion and pure combustion. Jinling Stone X has achieved success in the co-firing of coal and petroleum coke in a circulating fluidized bed. Considering the consumption of petroleum coke, burning it pure is more promising than mixing it with other materials. In 1992, the Nisco Thermal Power Plant in the United States built two circulating fluidized bed boilers that burned petroleum coke exclusively, with a capacity of 375 t/h each. This boiler was manufactured by the American company FW and burns high-sulfur petroleum coke supplied by Citgo and Conoco refineries. Since its operation began in 1992, the availability rate of its boilers has exceeded 90%, achieving satisfactory results. The main problem with the circulating fluidized bed boiler in the Nisco thermal power plant is slag formation at the inlet of the cyclone separator and at the J-valve, which results in a decrease in the boiler’s output and a short operating time. Another issue is the high-temperature corrosion of the central tube in the cyclone separator and the ash accumulation on the heated surfaces at the tail section; currently, there are no very effective solutions to these problems. In 2000, two 220 t/h CFB boilers that burn pure petroleum coke, manufactured using technology from the American company FW, were put into operation at the second thermal power plant of Zhenhai Refining & Chemical Co., Ltd.; these boilers used high-sulfur petroleum coke produced by the company’s delayed coking unit. Since its commissioning in 2000, this boiler has achieved an operation rate of over 90%, delivering excellent results. The main problems in boiler operation are the high carbon content in the fly ash (38.79%), easy clogging of the J-valves, and a short continuous operating time. Despite numerous modifications, the problem of high carbon content in fly ash has not been fundamentally resolved. In 2001, the first domestically produced medium-temperature and medium-pressure pure petroleum coke CFB boiler at Wuhan Petroleum Plant X was put into operation, using petroleum coke produced by Wuhan Petrochemical Plant X’s delayed coking unit. Since its trial operation, this boiler has undergone numerous modifications and adjustments, yet it has continued to struggle to achieve its rated output. The main reason is the low amount of return material, which results in a high bed temperature in the dense-phase zone; the temperature difference between the upper and lower parts of the bed is large, making it difficult to control the bed temperature. As a result, the boiler usually operates at only 70% of its rated capacity. The advantages and disadvantages of burning petroleum coke in circulating fluidized bed boilers are both evident. Its advantage is that the desulfurization process is carried out simultaneously with combustion, eliminating the need for a coal powder preparation step. However, its disadvantage is the high calcium-sulfur molar ratio; when the sulfur content in petroleum coke is 5%–6%, the amount of limestone required is approximately 40%–50% of that needed for petroleum coke. This necessitates the installation of systems for grinding and transporting limestone. The amount of slag generated is roughly equal to the amount of limestone used, and the slag has little practical value. The two CFB boilers at Zhenhai Refining & Chemical Company X consume 296 kT of high-sulfur petroleum coke per year, 130 kT of limestone per year, with an ash discharge volume of around 130 kT. In the 1970s, based on slag gasification technology, SHELL developed the pressurized pulverized coal gasification technology (SCGP), which enables \"zero emissions\" of pollutants. In 1993, an integrated gasification combined cycle power plant (IGCC) with a capacity to process 2,000 tons of coal per day was built in De Moerle, the Netherlands; it operated continuously for one year, overcoming the short operation cycle associated with the CFB process. Industrial tests were conducted on this device involving the addition of high-sulfur petroleum coke to coal powder, and success was achieved. Essentially, SHELL’s SCGP process involves the partial oxidation of coal or high-sulfur petroleum coke to produce crude syngas. The components of syngas are mainly hydrogen and carbon monoxide, in addition to CO2, H2S, COS, etc. Crude synthesis gas requires desulfurization using the low-temperature methanol washing process, with a desulfurization efficiency of up to 97%. The hydrogen sulfide that escapes can be converted into sulfur using the Claus process for sale. The desulfurized and cleaned syngas can be used as fuel for gas turbines to drive generators to produce electricity. The exhaust gas temperature from the gas turbine is approximately 500°C, which can be used to generate steam in a waste heat boiler. The syngas produced by the SCGP process can also be used as a raw material for hydrogen production. The carbon monoxide in syngas undergoes a shift reaction with water vapor in the presence of a catalyst to produce hydrogen and carbon dioxide; this gas is known as shifted gas. The transformed gas, whose hydrogen purity has been improved through pressure swing adsorption, can be used in hydrogenation units. The low calorific value off-gas produced by pressure swing adsorption can be used as an auxiliary fuel for boilers. Syngas can first meet the hydrogen production needs, with the excess used to generate electricity in gas turbines. With its suitability for the IGCC process, high-sulfur petroleum coke, which seemed on the verge of becoming obsolete, has once again become highly sought after. In the overall planning of numerous integrated refining and chemical projects in the country, priority is given to constructing combined partial oxidation/power generation/hydrogen production facilities that use high-sulfur petroleum coke as raw material. These facilities recycle refinery by-products while producing steam, hydrogen, and electricity to meet the needs of refining hydrogenation and ethylene cracking processes. The IGCC process is complex and difficult to control. Since this process uses pure oxygen, it requires the installation of large-scale air separation oxygen production units, which further increases the construction costs. However, from the perspective of comprehensive resource utilization, the IGCC process is currently a relatively ideal clean utilization method for high-sulfur petroleum coke.