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Application of High-Efficiency Methanol Condensers Wu Shuli, Tang Jianye, Wu Liyan (Shijiazhuang Tianren Chemical Equipment Group Co., Ltd., Shijiazhuang, Hebei 052160) Abstract: The traditionally used shell-and-tube methanol distillation condensers consume large amounts of water, and the circulation water pumps as well as the fans in the cooling towers require high levels of electrical power； Poor heat exchange leads to high vent temperature and increased alcohol consumption. After comparing and calculating various aspects of several types of heat exchangers, a high-efficiency methanol condenser was selected, which features high heat transfer efficiency, strong resistance to scaling, good corrosion resistance, as well as energy and water savings. Keywords: high-efficiency methanol condenser, shell-and-tube condenser, energy saving, reflux. Shell-and-tube condensers consume a large amount of water; the circulation pump and the fans in the cooling tower also use a lot of electricity. Moreover, they are prone to scaling and blockage when the water quality is poor or water treatment is inadequate, which leads to a decrease in heat exchange efficiency, higher vent temperatures, and increased alcohol consumption. Therefore, based on a comprehensive comparison of various types of heat exchangers and through thorough calculations, our company has designed and manufactured highly efficient methanol condensers. The equipment was tested in the methanol distillation section of Shijiazhuang Jinshihua Fertilizer Co., Ltd., and performed well, meeting the design requirements. 1. Operating principle of high-efficiency methanol condensers: The working principle of the TRCL series of high-efficiency methanol condensers is to feed the high-temperature methanol vapor that needs to be condensed into the heat exchange tubes where it is cooled, thereby causing the high-temperature vapor to condense into a liquid. The heat exchange process involves using a repeatedly reused cooling water source to continuously wet the surface of the heat exchange tubes, allowing some of the cooling water to absorb the heat from the condensed substance inside the tubes and then evaporate ； Heat is dissipated into the atmosphere by fans with stable performance and reliable operation. The cooled water that has not evaporated continues to dissipate heat through an efficient cooling device; after being cooled, it returns to the collection tank, where it is sent back to the spraying system by a circulation pump for repeated use. It is a new type of efficient condensation equipment that integrates water cooling with air cooling, as well as heat transfer and mass transfer processes, taking advantage of the strengths of both approaches. 2. Trial use of a high-efficiency methanol condenser in the refined methanol system’s condensation process 2.1 Design and selection of heat exchange equipment: ① Name: TRCL-3.0 type high-efficiency methanol condenser ② Capacity: Designed for a plant with an annual production capacity of 30,000 tons of methanol ③ Type and material of heat exchange tubes: Corrugated tubes, 0Cr18Ni9 ④ Design parameters: Main column reflux ratio: 2.5; Pre-column reflux ratio: 0.8 ⑤ Total installed power of operating equipment: 28 kilowatts 2.2 Construction and installation of equipment pipelines This high-efficiency condenser is installed at the location of the original high-level cooling tower in the circulation water pump room of Jinshi Company’s refined methanol production section. The existing old cooling tower was also removed; its height difference from the return tank was roughly the same as that of the original tube-type condenser. As part of the process modifications, in addition to adding a return pipeline, the existing vent pipeline was altered, and gas-liquid equilibrium pipes were added accordingly. During the renovation process, we conducted process calculations for the condensation system and determined the resistance of the system. Based on these findings, we adjusted the diameters and flow direction gradients of the inlet manifold, condensation exhaust pipes, condensation return manifolds, vent pipes, as well as the corresponding balance pipes of the high-efficiency condenser. The process parameters for the cooling fan and circulating water pump were also determined. 2.3 Test Procedure: Shijiazhuang Jinshi Chemical Fertilizer Co., Ltd. currently has two units for the production of pure methanol, with each unit having a designed capacity of 40,000 tons per year of pure methanol. A double-column distillation process is employed, using floating-valve columns; the actual maximum capacity of a single column can reach 25,000 tons of pure methanol. (To facilitate future expansion of methanol production, the capacity of the methanol condenser used in this test was increased.) This test utilized one of these units, with the existing tubular condenser in the main pre-distillation column being replaced by a more efficient condenser that combines functions with the main pre-distillation column. Since the test was conducted in early spring, to prevent issues such as excessive condensation or poor condensation reflux that could lead to water hammer or gas blockages, a step-by-step approach was adopted for the test, as follows: ① Fill the tank of the efficient methanol condenser with water. ② The high-efficiency methanol condenser circulation pump has been put into operation. ③ Gas is guided from the distillation tower to this condenser. ④ After backflow occurs, turn on the cooling fan. ⑤ The air and water supplies to the original shell-and-tube condenser are cut off, and the top of the distillation tower is fully condensed using a high-efficiency methanol condenser. ⑥ Control the amount of product extracted and conduct a full analysis of the extracted product. ⑦ Enable pre-tower condensation in the same way, and disable the original tubular condenser in the pre-tower. ⑧ Only air cooling tests were conducted during the water shutdown; the condensation temperature rose rapidly, so the water pump was turned back on. ⑨ Under light load conditions, a complete shutdown with only water spray testing was carried out, and the test result showed a significant decrease in load. Restore one fan to operation. The test results show that water shutdown causes smaller load fluctuations than air shutdown ⑩. Load flexibility tests were conducted, and the plant continued to operate normally when the output volume dropped to 3.2–3.5 cubic meters of pure methanol. Product quality is not affected. 2.4 Test data: Main column reflux ratio: 2.4–2.5; Pre-column reflux ratio: 0.7–0.8; Ethanol yield: 4.2–4.4 cubic meters; Condensation temperature in the main column: 42°C; Condensation temperature in the pre-column: 42°C; Ambient temperature during testing: around 15°C; Relative humidity during testing: 50%; Number of cooling fans in operation: one (out of three); Current consumption of the cooling fan: 16.5 A (within normal limits). 2.5 Product quality analysis: Appearance: colorless and transparent; Water solubility: clear; Color intensity: 5–10; Apparent density: 0.7870; Density: 0.7915; Dry point during distillation: 64.8°C; Distillation volume: 98.6 ml; Potassium permanganate test time: average of 45 minutes; Moisture content: 0.01%; Free alkali content: 0.0005%. The above are the test results. When the system operates under normal conditions, the potassium permanganate test time for the product exceeds 50 minutes, and the color intensity is 5, meeting the standards for high-quality products. 3. Test conclusions: ① The testing process of this high-efficiency methanol condenser proceeded quite smoothly; the switching time between the main pre-condenser and the original tubular condenser could be completed within one hour. Thanks to the well-improved external piping system, no issues such as gas blockage leading to poor backflow occurred during the tests, and the operation and control were simpler compared to the old system. ②The quality of the refined alcohol produced shows that the operation of this device has had no impact on product quality; in fact, some parameters are even better than those obtained with the original tubular condenser. ③This device achieves significant savings in electricity and water usage. In terms of energy savings, its total installed capacity is only 28 kilowatts; based on tests of power consumption, it can save more than 50% compared to the original circulating water pump system. Compared to the water replenishment in the original circulating water system, the water-saving effect can also reach over 50%. Based on these calculations, the economic benefits are quite significant. Preliminary estimates show that 480,000 kWh of electricity and 128,000 tons of water can be saved annually. Based on the rates applicable to the fertilizer industry in the Shijiazhuang area, the annual savings from energy and water conservation alone amount to 350,000 yuan (this figure does not include the costs associated with shutting down the tube-type condensers for cleaning, the losses resulting from reduced production capacity, nor the losses due to high vent temperatures that cause methanol loss). ④This unit is fully suitable for the efficient condensation of methanol; therefore, after 120 hours of trial operation, Jinshi Fertilizer Co., Ltd. has put it into regular production. Since trials began on March 6, 2006, and regular production started on March 11, the unit has been operating stably. One 155KW circulation water pump has now been shut down. At present, this ethanol purification unit (originally designed to produce 25,000 tons of ethanol per year) produces around 120 cubic meters of output per day, with all the product quality being of top grade. ⑤The use of high-efficiency methanol condensers can bring about a revolution in the design of methanol distillation units as well as in the expansion of existing ones. In new designs and expansions of existing methanol distillation plants, it is no longer necessary to build or expand pump rooms for circulating water; high-efficiency methanol condensers can be used instead. Due to the reduced need for maintenance, such equipment can be installed on the roof of the control room (for existing buildings, it is necessary to determine whether the building can bear the weight), thereby reducing the space required by the methanol distillation unit and the associated construction costs. In short, the application of this device takes the methanol distillation condenser to a new level.