TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The water in the methanol rectification tower is charged by pressure difference. The wastewater prepared at the tower kettle of the methanol rectification tower can be re-used, after cooling, as a heat exchange medium of a first condensing heat exchanger (12), a second condensing heat exchanger (17) and a third condensing heat exchanger (23). Preferred Parameters: The methanol rectification tower has an operational micro-pressure of 0.05-0.3 MPa, a control temperature at the tower top of 65-73 degrees C, and a control temperature at the tower kettle of 105-120 degrees C. The pre-rectification tower has an operational pressure of 0.6-1.2 MPa, a control temperature at the tower top of 46-75 degrees C, and a control temperature at the tower kettle of 130-145 degrees C. The dimethyl ether rectification tower has an operational pressure of 0.6-1.2 MPa, a control temperature at the tower top of 40-65 degrees C, and a control temperature at the tower kettle of 100-125 degrees C. Preferred Component: The catalytic synthesis device has a fluidized bed or isothermal row tube fixed bed reactor having an operational pressure of 0.6-1.2 MPa, an operational temperature of 260-300 degrees C and a liquid phase space velocity of 3-12 L/kg-hour. The reactor uses heat-conducting oil or high pressure hot water as a temperature control medium, where a deviation of hot pointing temperature with an average temperature of the reactor is not greater than 10 degrees C.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The catalyst for dehydration reaction of methanol is a solid acid catalyst. It is preferably active aluminum oxide, HZSM-5, de-aluminized Y-shaped molecular sieve, or aluminum titanate.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The methanol is industrial methanol. The methanol concentration of the wastewater prepared at the tower kettle of the methanol rectification tower is less than 50 ppm.