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0 Overview: Anhui Haoyuan Chemical Group Co., Ltd. is a large-scale coal chemical enterprise in China. It currently operates 4 sets of \"18·30\" ammonia synthesis units, among which System No. 1 was upgraded from an original ammonia synthesis unit with an annual capacity of 120,000 tons. The desulfurization section of this system consists of two filler desulfurization towers, No. 1 and No. 2, both with a diameter of Ф5M, operating in parallel. Tower No. 1 is 25 m high; it has two sections of packing, each about 13 m high, and all of the packing consists of Боул rings with a diameter of Ф76 ； Tower 2 has a height of 28.5 m. Each of the two desulfurization towers is equipped with two Ф7m regeneration tanks, along with a lean liquid pump and a rich liquid pump with a capacity of 480 m3/h. 1 Existing problems: As production capacity increased, this system gradually exhibited two major problems, one of which was low desulfurization efficiency. It is only possible to operate under low-sulfur conditions with hydrogen sulfide levels in the semi-water gas ranging from 0.5 to 0.9 g/m3; when the H2S level before desulfurization is ≥1 g/m3, the H2S level after desulfurization exceeds the allowable limit. There are no means to address this issue, and such levels are far from meeting the requirements for the current raw coal. Second, the tower blockage is severe. Under normal circumstances, after about 5 to 6 months of operation following maintenance, the resistance of the tower begins to increase, and it becomes necessary to shut down the plant and dismantle the tower after 15 to 18 months. It not only fails to ensure continuous operation over long periods of time in production, but also has a certain impact on environmental protection. Therefore, it is imperative to upgrade this desulfurization system. 2. In terms of the renovation approach, considering the possibility and necessity of further reducing hydrogen sulfide levels in semi-water gas in the future, and in order to enhance the flexibility of the desulfurization system, Haoyuan Company decided to change the configuration from two parallel towers to two series-connected towers. After thorough investigation and evaluation, it was decided to use the empty-tower spraying technology developed by our company in Tower 1, which has been modified to serve as a pre-desulfurization tower. Our company will provide a technical renovation plan. After the two towers were changed from parallel to series configuration, the gas flow rate per tower doubled compared to before. Based on process calculations, for the packed desulfurization tower, the gas velocity in the empty tower is somewhat high, but it remains within the upper limit and not much above it. For an empty tower, the gas velocity range can be appropriately larger. Therefore, this is also the prerequisite for changing the configuration of the two towers from parallel to series. 3 Technical parameters: Haoyuan Chemical provides the following technical parameters: Flow rate of semi-water gas to be treated: 74,000 Nm3/h; Inlet H2S concentration: ≥4 g/m3. The required H2S concentration at the outlet of Tower No. 1 after modification is ≤1.0 g/m3. The backpressure after the modification of Tower No. 1 should be ≤10 gmmHg. It is necessary to ensure that the desulfurization efficiency and system backpressure do not change by more than 10% over a period of three years. Desulfurization solution loss: V_loss ≤ V_circulation × 0.5%/day. 4. Technical Solution: Based on the technical parameters and requirements specified by Haoyuan Chemical, our company has formulated the following renovation plan: (1) The existing 1# Ф5m old desulfurization tower will be modified, with the original packed tower being converted into a spray tower. According to calculations, 80 sets of DSP-18 high-efficiency atomizing nozzles developed and produced by our company are required; each nozzle has a flow rate of 18–20 m3/h. The total solution circulation rate needed is approximately 1600 m3/h. (2) Three new desulfurization pumps with a flow rate of 800 m3/h and a head of 70m will be installed (2 in operation, 1 as backup); the existing pumps can be used as regeneration pumps. (3) Due to the significant increase in the solution circulation rate, the regeneration residence time in the existing regeneration tanks is no longer sufficient; calculations show that regeneration tanks with a diameter of Ф9000 are required, along with 34 injectors of Ф30, resulting in a regeneration residence time of about 15 minutes. (4) Install liquid-lean tanks and liquid-rich tanks that are suitable for the process. (5) Sulfur recovery system: Since the amount of hydrogen sulfide processed per unit time has increased significantly after the modification, and the volume of residual liquid recovered after continuous sulfur melting is large, it is recommended to filter the sulfur foam before melting it, which also helps to reduce clogging of the nozzles. 5 On-site implementation: With the joint efforts of the technical and production management personnel from both parties, the renovation plan was put into effect in late February 2011, and the installation was completed after 40 days. The discrepancies between the actual modification and the planned modification are as follows: (1) From the perspective of maximizing the utilization of high-desulfurized coal, Боул rings with a diameter of Ф76 and a height of about 1 m were installed in the lower section of the tower. (2) To address the high solution loss caused by foam entrainment, the swirl plate demister at the upper part of the tower was not removed. (3) Due to space constraints and other reasons, Haoyuan Chemical did not build a new Ф9000 regeneration tank as recommended by our company; it also did not enlarge the lean liquid tank or the rich liquid tank, but instead installed three new lean liquid pumps with a capacity of 800 m3/h each. 6 After the installation was completed, the desulfurization system was connected to the grid and put into operation at the beginning of May, operating in a tandem configuration with two towers. After operation, when the H2S concentration at the inlet of the desulfurization tower was around 1.5 g/m3, with only one pump operating and 42 nozzles in use, the H2S concentration after desulfurization was 0.5 g/m3, resulting in a desulfurization efficiency of over 60%. At the same time, the tower resistance is ≤10 mmHg, which basically meets the design requirements as well as the technical specifications of Haoyuan Chemical. In September 2012, when the author returned to Haoyuan Chemical for a technical follow-up visit, the H2S level before desulfurization had already reached over 2 g/m3. With only one pump in operation and 70 nozzles in use, the desulfurization efficiency was around 75%. Furthermore, after several months of operation, the tower resistance remained at 10 mmHg, with no signs of an increase in tower resistance. Both company leaders and workshop managers have expressed satisfaction. 7 Problems and Discussions: Due to the large diameter of the tower, the diameter of the upper ring tubes is also large, and there is only one upper liquid supply pipe; this makes it easy for the nozzles at the ends of the ring tubes to become clogged. The author suggests that when upgrading towers with a diameter greater than 4.5 meters, it would be advisable to use two upper liquid supply pipes in order to prevent clogging at the ends of the ring tubes. 8 Conclusion The successful application of the combined process of empty-tower spraying and series-packed towers in Haoyuan Chemical’s System 1 once again proves that the empty-tower spraying technology developed by our company is mature, reliable, and holds great potential for widespread adoption.