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1 Overview: Henan Jinkai Group Yanhua Chemical Co., Ltd. is a comprehensive chemical enterprise that primarily produces synthetic ammonia, methanol, and urea, while also manufacturing products such as heat and power generation facilities and plastic woven bags. Starting as a small plant with an annual synthetic ammonia production capacity of 3,000 tons, it has developed through successive expansions over the years; today it boasts an annual production capacity of 280,000 tons of ammonia-based products, of which 120,000 tons are methanol and 300,000 tons are urea. The company is also capable of generating 200 million kWh of electricity per year, making it a medium-sized enterprise in the nitrogen fertilizer industry. In particular, after being taken over by Jin Kai Group, it injected strong momentum for the company’s development. The approval process for the company’s “6080” project has now been completed, and the project can be implemented by the end of 2012. Over the years, the company has attached great importance to the removal of hydrogen sulfide. However, as production capacity increased and the types of raw coal changed, the H2S content in the shift gas rose significantly, resulting in H2S levels exceeding limits even after desulfurization of the shift gas. Furthermore, the increased load on the degassing tower leads to more frequent blockages, forcing shutdowns to clean the tower and its packing, which has a severe impact on production. 2 Determination of the technical solution: Due to the severe corrosion of the currently in use ￠3800 variable pressure distillation column, the company decided to replace it with a new column. Regarding the structural design to be adopted for the new tower, the company established a project evaluation team composed of units such as the Technology Development Department, the Production Department, and the transformation and stripping workshop, and conducted detailed inspections at sister manufacturers. After thorough consideration, it was decided to use the filler-free tower technology developed by Changchun Dongshi Science and Trade Co., Ltd. – the QYD composite high-efficiency mass transfer internals – for the new transformed gas desulfurization tower. According to the renovation plan provided by Changchun Dongshi Science and Trade Industry Co., Ltd., the implementation will take place during the system maintenance period at the end of 2011. 3 Main technical parameters: Reformer gas flow rate: ≤65000 m3/h; Operating pressure of the reformer tower: 0.8 MPa; H2S content in the reformer gas: ≤350 mg/Nm3; H2S content at the outlet of the reformer unit: ≤10 mg/Nm3; Resistance of the reformer tower: ≤30 KPa; Reformer pump: Flow rate of 315 m3/h, head of 150 meters. 4 The structure and working principle of the QYD composite mass transfer internals: Considering the actual conditions of the conversion process, the hydrogen sulfide concentration at the inlet is relatively high. To achieve more satisfactory results, this conversion and removal tower adopts a composite tower design that combines the QYD internals technology with tray spraying technology. The upper half of the tower is equipped with three layers of QYD internals, while the lower half features a dry tower spray section fitted with 20 high-efficiency atomizing nozzles. The working principle of this tower is as follows: The QYD composite internal component consists of four parts: a gas distribution device, a bubble redistribution device, a downcomer, and a liquid holding section formed after assembly. The gas flow path in this device is as follows: first, the shifted gas enters from the bottom of the tower, where it comes into counter-current contact with the atomized desulfurization liquid sprayed by the nozzles in the spraying section, thereby enabling preliminary purification of the shifted gas. Then, the treated gas enters the first gas distribution device in the tower, where it undergoes bubbling mass transfer absorption with the desulfurization liquid flowing from top to bottom within the liquid holding section; at this point, hydrogen sulfide in the gas rapidly reacts with the desulfurization liquid through bubbling absorption. Thereafter, the gas rapidly enters the second and third gas-liquid distribution layers from bottom to top, undergoing the same hydrogen sulfide absorption reaction as in the first layer; at this point, the gas desulfurization efficiency has reached over 95%. Finally, the gas passes through a demister to remove the liquid droplets carried in the bubbles, after which it exits the tower and proceeds to the next processing step. The flow of the liquid within the tower is as follows: the desulfurization liquid enters the third liquid-holding section at the upper part of the tower, where it undergoes gas-liquid bubbling absorption reactions. After absorbing some H2S, it overflows into the downcomer and is then carried to the second liquid-holding section. The desulfurized liquid exits through the downcomer again, entering the first liquid-holding section to undergo the same gas-liquid mass transfer absorption process. Finally, the desulfurized liquid exits from the bottom of the tower and is depressurized before being sent to the oxidation regeneration tank. 5 Implementation of the technical solution: At the beginning of November 2011, the company took advantage of the annual maintenance period to install the internal components of the distillation tower. At the same time, Dongshi Company sent Engineer Wang for on-site technical guidance to assist the installation company with the installation of the internal components of the ¥3800 transformer degassing tower. The basic installation configuration of the tower is that a spray section at the lower part of the tower is provided (equipped with twenty high-efficiency atomizing nozzles distributed evenly). The QYD type gas-liquid mass transfer device has a three-layer arrangement; each layer’s liquid holding section is 1 meter high, and there are two Φ426 downcomers per layer. On November 10, the system was started up; the flow rate of the gas entering the tower for conversion was 55,000 m3/h, with a H2S content of 320–390 mg/Nm3. The H2S content in the gas exiting the tower was 5–10 mg/Nm3. The resistance in the conversion and removal tower was around 22 KPa, and the spray section at the bottom of the tower was not in operation. However, as the production load increased, when the flow rate of the gas entering the tower reached around 65,000 m3/h, the H2S content in the gas exiting the tower was between 15 and 20 mg/Nm3, which deviated from the design value (the required H2S content at the exit of the reactor: ≤10 mg/Nm3). The spray section at the lower part of the tower cannot operate for the time being due to the small size of the liquid outlet pipe from the regeneration tank. After communicating with Engineer Wang from Dongshi Company, it was determined that the catalyst currently in use is not suitable for removing high levels of sulfur. The catalyst was replaced at the beginning of May this year. After nearly a month of operation monitoring, under full-load conditions, the H2S concentration at the inlet to the tower was around 250 mg/Nm3, the H2S concentration at the outlet was between 6 and 8.5 mg/Nm3, and the tower pressure drop was around 22 KPa. To date, the transformation system has been operating quite stably. Given that the hydrogen sulfide level in coal will increase to around 400 mg/Nm3 in the future, and in order to meet the requirements of chemical production, the company plans to take advantage of maintenance opportunities to modify the outlet pipe of the regeneration tank. At the same time, a desulfurization pump with a capacity of 200 m3/h will be added for use in the spraying section, thereby ensuring the long-term stable operation of the desulfurization system. 6 Actual Operating Results 6.1 The operating conditions of the original filler in the desulfurization tower are shown in the table below. 6.2 The operating conditions of the QYD composite mass transfer internals in the desulfurization tower are also shown in the table below. Since the commissioning of the desulfurization system by Jin Kai Yan Hua Company in November 2011, fairly satisfactory results have been achieved; the table below shows the operating conditions as of June 2012. 6.3 Material Consumption and Economic Benefits Due to the reduction in H2S levels after the implementation of this desulfurization method, the activated carbon desulfurizer can now be used for one to two years instead of three months, resulting in annual savings of 1–2 million yuan. More importantly, the unique design of the QYD composite high-efficiency mass transfer internals prevents tower blockage more effectively, avoiding the need to remove the packing during system shutdowns; thus, the indirect economic benefits it brings to enterprises are quite significant. 7 Conclusion In summary, the application of the QYD composite high-efficiency mass transfer internals in Jin Kai Yan Hua Company has been quite successful. This internal component makes full use of the rapid chemical reaction mechanism between H2S and alkaline solutions, combining the advantages of various mass transfer components such as traditional bubble towers, bubble cap towers, sieve plate towers, counter-current plate towers, and packed towers. It enhances the gas-liquid mass transfer process by facilitating dynamic contact between the gases and liquids as well as turbulent mass transfer, thereby increasing the gas-liquid contact area and significantly improving the purity of the gases. More importantly, it fundamentally solves the problem of tower blockage in desulfurization towers. This internal component is suitable not only for the renovation of existing towers, but also when designing new towers, it helps to save around 30% on investment costs. Therefore, the QYD composite high-efficiency mass transfer internals are currently the most valuable gas-liquid mass transfer internals for use in shift gas desulfurization towers.