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1 What are the options for the production process and scale of dimethyl ether at Weihua? The first phase of Weihua’s facility uses coal as raw material, and employs Texaco’s water-coal slurry pressurized gasification technology to produce 300kt of synthetic ammonia per year, which is then used to manufacture 520kt of urea as a fertilizer. Therefore, the ongoing methanol project still uses bituminous coal as raw material, employing a water-coal slurry pressurized (6.5 MPa) gasification process to produce syngas. It is equipped with some shift and low-temperature methanol washing units to prepare the gas required for methanol synthesis, and uses an isobaric synthesis process to produce 200 kt of methanol per year. In selecting a technical approach for dimethyl ether synthesis, we examined several gas-solid one-step synthesis processes developed in China, as well as the slurry bed process. Although the one-step process has the advantage of a high one-way conversion rate for carbon monoxide, most of these processes are still in the experimental stage, with no large-scale industrial facilities yet in operation. The gas-solid phase catalytic dehydration process for methanol yields products of high purity, features flexible process design, and benefits from extensive industrial operation experience; several large-scale dimethyl ether projects worldwide have adopted this two-step gas-solid phase dehydration process. Therefore, this factory has chosen the gas-phase methanol dehydration technology for dimethyl ether production, which was developed by the Southwest Chemical Research Institute. ? Additionally, despite the wide range of applications for dimethyl ether, global production and demand levels remain around 150–200 kt/year, and it is still used primarily as an aerosol propellant and as a chemical raw material. The development of dimethyl ether in China started relatively late; although demand for it in the production of aerosols is increasing, the total demand remains around 30–50 kt/year. As an ether fuel, the market for dimethyl ether remains uncertain; therefore, the production capacity for dimethyl ether has been set at 10 kt/a, which is the highest among the existing and under-construction facilities in China. It mainly produces dimethyl ether. Its product specifications are shown in Table 1. 2 Brief description of the process flow: Methanol from tank V2901 is heated by pump preheater E2904, and then sent to vaporization tower T2901 for vaporization. The vaporized methanol passes through heat exchanger E2903 before entering reactor R2901 in two streams; the first stream of methanol vapor is heated to the reaction temperature and enters the reactor from the top ； After being slightly superheated, the second stream of methanol vapor enters the reactor from the middle as a cooling gas. The crude dimethyl ether exiting the reactor is cooled by heat exchanger E2903, preheater E2904, and water cooler E2905 before entering the crude dimethyl ether storage tank V2902, where gas-liquid separation takes place. The liquid phase consists of dimethyl ether, while the gas phase contains non-condensable gases such as hydrogen, carbon monoxide, methane, and carbon dioxide, along with saturated dimethyl ether and methanol vapors. The gas-phase material enters the methanol scrubber T2902, where dimethyl ether is absorbed using methanol. The absorbent solution is returned to the crude dimethyl ether storage tank, while the exhaust gas after absorption is sent for combustion in a flare under reduced pressure. ? The crude dimethyl ether in the crude dimethyl ether tank is sent to distillation tower T2903 by pump P2903. The dimethyl ether product drawn from the bottom of a section of packing in T2903 enters the metering tank by natural flow, and is then pumped into the product storage tank V3101. The bottom liquid from the distillation tower is discharged into V2903 and then sent back to the methanol vaporization tower, where the recovered methanol is reused. The process wastewater from the methanol vaporization tower is cooled by water cooler E2909 before being sent to the coal mill in the water-coal slurry gasification unit for use. ? 3 Technical features? (1) The catalyst used is the CNM-3 type, developed by the Southwest Research Institute itself; it mainly consists of γ-Al2O3 and SiO2, with a small amount of auxiliary catalysts. The physical properties of this catalyst are as follows:? ① Dimensions: φ3–4×10–20 mm, cylindrical shape? ② Bulk density: 0.7 kg/L? ③ Specific surface area: 150–300 m2/g? ④ Average pore size: 4–6×10‑6 mm? ⑤ The primary conversion rate of methanol exceeds 70%, while the selectivity for dimethyl ether is greater than 99%. The service life of this catalyst is 1–2 years. http://www.nmtech.com.cn/jishuwang/upload/0601261107293007.jpg Figure 1: Schematic diagram of the dimethyl ether production process. (2) The vaporization and recovery of methanol are combined into one step, which saves both investment costs and energy consumption. ? (3) High-efficiency plate corrugated structured packing is used in the vaporization tower, alcohol washing tower, and distillation tower. ? (4) The emitted waste gases are burned in an eternal flame torch; the waste methanol is collected separately, and the wastewater is sent to the gasification coal grinding unit for recovery, thereby eliminating environmental pollution. ? (5) Since the product is high-purity dimethyl ether, to ensure purity, the distillation tower as well as the equipment and piping used in subsequent processes are all made of stainless steel. (6) The pump used for transportation is a shielded pump with excellent sealing performance. ? The raw materials and energy consumption are shown in Table 2. ? http://www.nmtech.com.cn/jishuwang/upload/0601261108234898.jpg