Application of mechanized construction in the rapid reconstruction of sulfur incinerators

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This post was last edited by liaifeng on 2018-8-4 at 19:56. As time goes by, the service life of sulfur incinerators in China is coming to an end, and there is a need to rebuild these incinerators. Whether it is a sulfur furnace for acid production from sulfur or a boiling furnace for acid production from pyrite, any local damage, detachment, cracking, or similar issues in the refractory brick lining are very difficult to address. From removing the refractory bricks, rebuilding them, drying the furnace to finally starting up the operation with materials fed in, it takes at least 2 months. Considering the impact of weather conditions on rebuilding, and while ensuring the quality of the furnace, the actual construction time often requires 3 months or even longer. The long reconstruction period for sulfur incineration furnaces affects and delays the annual major maintenance schedule of the sulfuric acid production plant, resulting in economic losses. Taking a set of 400 kt/a sulfuric acid production plants as an example, apart from the costs associated with rebuilding the sulfur incineration furnaces, expenses such as the purchase of sulfuric acid from external sources, employee salaries, and asset depreciation alone result in losses of 80,000 to 100,000 yuan per day. Over a period of 2 months, this amounts to economic losses of 4.6 million to 6 million yuan, which is far higher than the total cost of the sulfur incineration furnaces. If one also takes into account the loss of the peak marketing season, which affects the achievement of the annual sales targets, the negative impacts are immeasurable. 1. Forcing a reduction in the project timeline leads to painful consequences. The problems associated with rebuilding sulfur burners are often more complex and variable than those encountered during new construction. Owners, seeking to shorten the time required for maintenance, tend to drastically reduce the timeline for rebuilding sulfur burners, considering a shorter duration as an important factor in the bidding process; the party that can complete the project in the shortest time has a greater chance of winning the bid. And the contractor, eager to win the bid, also compresses the timeline as much as possible. This **increases the workload of the construction workers and enhances the impact of human factors on the quality of the furnaces. There was once a case where the reconstruction of a sulfur incinerator was completed in just 27 days (time taken for demolition and construction, excluding furnace drying), but only 3 months after it was put into operation, a serious quality issue occurred: local temperatures as high as 380 °C appeared on the top of the sulfur incinerator. To ensure everything was foolproof, the engineering department sent technicians in advance to various highly skilled furnace-building companies to conduct inspections and learning, and studied and analyzed their construction methods and techniques in detail. Before starting work, the engineering department established a dedicated project team for the sulfur incinerator. Team members took turns working day and night, ensuring 24/7 continuous construction of the sulfur incinerator without any interruptions. After the sulfur incineration furnace was heated up, a comprehensive inspection was carried out, and all parameters met the required standards. Moreover, the construction was scheduled for the pleasant month of October, allowing the impact of weather conditions on the quality of the furnace to be ignored. However, practice has shown that when using traditional masonry or casting methods to build furnaces quickly, it is difficult to ensure the quality of the furnaces. 2 Difficulties in rebuilding the sulfur incinerator: 1) The sulfur incinerator is a confined space, and manually removing the hazardous lining poses a significant risk; the brick lining can collapse, leading to casualties. After years of high-temperature sintering, the furnace lining has high strength and is difficult to remove ； The amount of refractory bricks that need to be removed and transported is between 300 and 400 tons, representing a huge workload. Relying solely on manual labor is time-consuming and labor-intensive, and it is not possible to meet the requirements for rapid reconstruction. 2) After years of use, the furnace shell of the sulfur incineration furnace often becomes distorted as a whole, resulting in a **reduction in the ellipticity of the shell. Engineering practice has shown that if the ellipticity deviation of the furnace shell is large, it has an adverse effect on on-site installation and alignment, the bricklaying of the furnace body, as well as on the proper operation of the burner and the normal functioning of the acid gas combustion furnace. 3) Weather conditions affect the project timeline and construction quality. Winter construction begins when the average daily outdoor temperature remains below 5 ℃ for 5 consecutive days, or when the lowest daily temperature drops below 0 ℃. When constructing industrial furnaces, it should be done in a heated environment, with both the working area and the area surrounding the masonry having temperatures of at least 5 °C. The mixing of refractory slurries and refractory castables should take place at temperatures of not lower than 5 ℃, while the temperature of refractory materials and precast blocks should be above 0 ℃ before they are used in construction. This has a significant impact on the reconstruction of sulfur-burning furnaces in winter; waiting for the weather to warm up delays the construction process, while forcing rapid construction does not guarantee the quality of the furnaces. In fact, working too quickly can lead to safety accidents such as collapses and injuries. 3. Application of mechanized construction in the reconstruction of sulfur incineration furnaces: With the progress of time and ongoing technological advancements, mechanized construction for large-scale furnaces is bound to replace traditional construction methods – this is an overall trend in the development of human technology. With the continuous upgrading of mechanical equipment and the ongoing development of refractory materials, the use of mechanized construction in the reconstruction of sulfur incineration furnaces has now become a reality and has been tested in practice. Mechanized construction can **reduce the construction period, lower the workload on workers, and ensure the quality of furnaces. Mechanized construction is divided into two parts: mechanized demolition and mechanized furnace construction. 3.1 Mechanized Demolition: In the mechanized demolition method, the end plates of the sulfur incineration furnace are first cut away using gas welding, thereby converting the confined space into an open one. A CAT mini-excavator is then used to enter the furnace for demolition and removal tasks. The key points are as follows: 1) The furnace must be shut down, and any hazardous substances must be removed or the space exposed to air at normal temperature; work can proceed only after on-site inspection and approval by the owner, the contractor, and the supervisor. 2) There is a lot of dust during demolition, so measures should be taken to spray water to control dust. There must be a place to dispose of the waste lining material, and the surrounding equipment needs to be protected. 3) After removing the end plates that were reused, the old lining material taken out is used to create a small slope, facilitating safe entry and exit for small excavators as well as loading by the waste lining material transport vehicle. 4) It is necessary to provide proper safety protection for the drivers, proceed with careful dismantling, and prevent injuries caused by collapses. To ensure the safe entry and exit of vehicles (including waste transport vehicles), one should board first, then move to the sides, and finally disembark. 5) In cases where it is difficult to remove the existing lining, the space is limited, and the risk level is high, the Swedish BROKK robot can be used to carry out the demolition of the sulfur incineration furnace, thereby preventing casualties (as shown in Figure 1). Figure 1: Demolition site of the BROKK robot in Sweden. 3.2 Mechanized furnace construction: Mechanized furnace construction makes use of the spray pouring technique, in which large quantities of material are pneumatically transported to high heights or distant locations via delivery hoses, enabling continuous construction of the furnace walls. It is a new type of mold-free construction technique characterized by a high degree of mechanization, fast construction speed, and the ease of installing labyrinthine expansion joints. It ignores the \"deformation and warping\" of the furnace shell, thereby minimizing the impact of human factors on the construction quality. As shown in Figure 2. Figure 2: Site of refractory spray pouring for the reconstruction of Hubei Yihua Group’s 330 kt/a sulfur incinerator – an example of mechanized construction of furnaces. Mechanized construction of furnaces is fast, as has been proven through practice, with real-world examples to support this. The spray casting technique was employed in the reconstruction of 1 set of 330 kt/a sulfur incinerator at Hubei Yihua Group, as well as in the construction of 1 set of 60 kt/a WSA wet-process acid production hydrogen sulfide incinerator at Shandong Luxi Chemical Group. The construction time for these furnaces was only 15 days, enabling rapid mechanical construction of the furnaces; details are shown in Table 1. Table 1 Cases of Mechanized Construction for Furnaces. Construction Date: Case 1, Case 2. Companies Involved: Hubei Yihua Group, Shandong Luxi Chemical Group. Project Content: Reconstruction of sulfur combustion furnace, construction of new hydrogen sulfide combustion furnace. Construction Period: August 2016, January 2017. Plant Capacity/(kt·a-1): 330, 60. Volume of Work/t: 350, 153. Weather Conditions: August in summer, January in winter. Construction Locations: Yichang, Hubei; Liaocheng, Shandong. Personnel Allocation/(shifts·d-1): 1) 2, 1. Planned Construction Duration/d: 50, 38. Demolition Time/d: 4. Furnace Construction Time/d2): 15, 15. Furnace Drying Time/d: 12, 12. Cooling Time/d: 4, 7. Total Construction Duration/d3): 35, 34. Note: 1) In Case 1, 2 shifts per day were used for 8 days; since sufficient time was available, the schedule was changed from 2 shifts per day to 1 shift per day ； 2) In Case 2, there was a 1-day power outage during construction, resulting in an actual construction period of 14 days ； 3) Case 2 was completed in January 2017, and the furnace drying was carried out in July. As can be seen from Table 1, with the help of mechanical equipment, even if workers are assigned to work one shift per day, the entire furnace construction can be completed easily within 15 days. This **reduces the workload on the construction workers and ensures the quality of furnace construction. From another perspective, there is still significant potential for improving the speed of mechanized construction. Mechanized construction of 5 kilns reduces the impact of weather factors; weather has a much lesser effect on mechanized construction. In the past year alone, furnace construction using mechanical methods has been put to the test by weather conditions in two extreme scenarios: hot and rainy summers in the south, and cold winters in the north. Under conditions of high temperatures and heavy rainfall in summer, as well as low temperatures and freezing in winter, mechanical construction still enables rapid furnace construction within 15 days; moreover, the overall timeline for demolition, furnace construction, and heating up can be completed within 35 days. This provides the best assurance for rebuilding sulfur incineration furnaces under extreme weather conditions in both summer and winter. Of course, these two types of weather conditions—cold and hot—do not have no impact at all on mechanized construction. High temperatures in summer cause the cooling process after firing to be slower, thereby prolonging the firing time, while low temperatures in winter make it impossible to carry out construction at night. 6 Safe Overwintering After Furnace Construction – Case 2: After completing the construction of its furnace, Shandong Luxi Chemical Group did not start operating it immediately; instead, it took winter maintenance measures by sealing the manholes and installing heaters inside the furnace to keep the temperature there above 5 °C (the actual temperature was 14 °C). This approach ensured a safe overwintering period, and the furnace was put back into operation after 6 months. Application and service life of mechanized construction for kilns: Mechanized construction of kilns not only **increases the construction speed but also ensures the quality and service life of the kilns. To date, 14 furnaces in China have adopted the spray pouring technique; to this point, there has never been a case where furnace quality issues caused owners to shut down their operations, which effectively ensures the stability of production for these owners. See Table 2 for details. Table 2 Application Scope and Service Life of Mechanized Furnace Construction
Unit: Furnace and Scale, Construction Year, Service Life

Hubei Yihua Group: 600 kt/a sulfur combustion furnace – side walls; 2006; 10 years
Hubei Yihua Group: 80 kt/a pure oxygen sulfur combustion furnace using insurance powder; 2009; 8 years
Hubei Yihua Group: 40 kt/a pyrogenic sulfur combustion furnace; 2010; 7 years
Xinjiang Yihua Chemical: Ammonia synthesis shift reactor; 2011; 6 years
Hubei Sanning Chemical: 100 kt/a hot air furnace; 2012; 5 years
Hubei Yihua Group: 600 kt/a sulfur combustion furnace and flue box; 2012; 5 years
Hubei Yihua Group: 800 kt/a sulfur combustion furnace and flue box; 2012; 5 years
Hubei Xingfa Chemical: 800 kt/a sulfur combustion furnace; 2012; 5 years
Hubei Yihua Group: 330 kt/a sulfur combustion furnace; 2014; 3 years
Hubei Zedong Chemical: 350 kt/a circulating fluidized bed boiler; 2015; 2 years
Hubei Yihua Group: 400 kt/a sulfur combustion furnace and flue box; 2016; 1 year
Hubei Yihua Group: 300 kt/a sulfur combustion furnace (reconstructed); 2016; 1 year
Shandong Luxi Chemical: 500 kt/a sulfur combustion furnace, flue box, and air preheater; 2016; 1 year
Shandong Luxi Chemical: 60 kt/a hydrogen sulfide combustion furnace; put into operation in 2017

Conclusion: Through more than 10 years of continuous practice and improvement, the mechanized construction of furnaces has become increasingly mature and reliable. This approach enables it to effectively shorten the construction time for reconstructing or building new sulfur combustion furnaces, while still ensuring high construction quality. As a result, the overall maintenance time is reduced, thereby providing a solid guarantee for the stable operation of production facilities.