NOVELTY - Fuel of rectified dimethyl ether is prepared by vaporizing methanol stored in a methanol raw material tank (1) using a methanol vaporization device (4); dehydrating the methanol by carrying out a dehydrating reaction of methanol steam in the presence of a catalyst at 260-300 degrees C under a work pressure of 0.6-0.8 MPa in a synthesis reactor (6) to prepare raw dimethyl ether; separating dimethyl ether and aqueous methanol solution through double-tower rectification; and rectifying and separating methanol and water.    USE - Process for combined preparation of fuel of rectified dimethyl ether (claimed).    ADVANTAGE - The process is environment-friendly and energy-saving; and has a methanol conversion of 75-85% in a single route of the process, and a dimethyl ether selectivity of not less than 99.5% (all claimed). It uses a solid acid catalyst with fine activity at low temperature; uses a component fluidized bed or isothermal row tube fixed bed reactor in which the reaction temperature is easily controlled; completely uses the reaction heat of the step of dehydrating methanol; prepares fuel of rectified dimethyl ether and chemical dimethyl ether with different prepared ratios by adjusting the reflux ratio of dimethyl ether pre-rectification tower to dimethyl ether rectification tower and produced ratio of tower top to side route; and uses totally sealed rectification to avoid releasing gas to exhaust. The wastewater can satisfy the discharge standard, which is safe and environment-friendly.    DETAILED DESCRIPTION - Combined preparation of fuel of rectified dimethyl ether includes:    (A) vaporizing methanol by storing methanol as raw material into a methanol raw material tank (1) with a flow quantity that is 4 times more than a consumption speed of technical methanol through a methanol transmission pump, carrying out heat exchanging of methanol from the methanol raw material tank with a mixture prepared by dehydrating methanol from a tower top of a synthesis reactor (6) through a methanol pump (2), subsequently transmitting into a methanol vaporization device (4) for vaporization in which the temperature of saturated steam of vaporized methanol is 130-140 degrees C and the pressure is 0.6-1 MPa, carrying out heat exchanging of methanol steam with the mixture prepared by dehydrating methanol from the tower top of the synthesis reactor by a heat exchanger (5) and transmitting into the synthesis reactor from the bottom in which the temperature after exchanging heat is 195-205 degrees C;    (B) dehydrating the methanol by carrying out a dehydrating reaction of methanol steam in the presence of a catalyst at 260-300 degrees C under a work pressure of 0.6-0.8 MPa in the synthesis reactor to prepare raw dimethyl ether, carrying out heat exchanging of the mixing steam from the top of the synthesis reactor with the vaporized methanol, then carrying out heat exchanging with a kettle liquid at the bottom of a methanol rectification tower (9), and finally carrying out heat exchanging of methanol solution pumped from the methanol pump at a heat exchanger (3), where the temperature of mixing steam after carrying out heat exchanging is less than 120 degrees C;    (C) separating dimethyl ether and aqueous methanol solution through double-tower rectification by transmitting the mixing steam carried out through heat exchanging for three times from the tower top of the synthesis reactor into a dimethyl ether pre-rectification tower (14) from a middle part for separating and purifying after cooling, thus preparing fuel of rectified dimethyl ether at the tower top of the pre-rectification tower in which the mass ratio of prepared fuel of rectified dimethyl ether to fuel of rectified dimethyl ether refluxed to the pre-rectification tower is 0.2-1.5 or transmitting into the pre-rectification tower in which the mass ratio of dimethyl ether flowing into the methanol rectification tower and the pre-rectification tower is 1-4, transmitting the dimethyl ether collected at a side route of the pre-rectification tower into a dimethyl ether rectification tower (20) in which the mass ratio of dimethyl ether collected at the tower top to the side route of the pre-rectification tower is 0.2-1.5, preparing the fuel of rectified dimethyl ether at the top of the dimethyl ether rectification tower, collecting the chemical dimethyl ether at the side route in which the dimethyl ether kettle liquid mixed with methanol is remained in the dimethyl ether rectification tower, transmitting the kettle liquid to the dimethyl ether rectification tower, or returning it to the pre-rectification tower in which the mass ratio of the dimethyl ether returning to the pre-rectification tower to the dimethyl ether returning to the dimethyl ether rectification tower is 1-4; and    (D) rectification and separation of methanol and water by transmitting the kettle liquid at the tower kettle of the pre-rectification tower into the methanol rectification tower, preparing methanol at the top of the methanol rectification tower, returning the methanol at the tower top into the methanol rectification tower, or returning it into the methanol raw material tank in which the mass ratio of methanol returning into the methanol rectification tower to the methanol returning into the methanol raw material tank is 0.3-1.4, preparing wastewater at the tower kettle of the methanol rectification tower, returning the wastewater into the methanol rectification tower by a re-boiler (8), or discharging it in which the mass ratio of the methanol returning into the methanol rectification tower to the methanol that is discharged is 0.5-1.5    .    DESCRIPTION OF DRAWING(S) - The drawing is a schematic flow diagram of a system for combined preparation of fuel of rectified dimethyl ether (Drawing includes non-English language text).    Methanol raw material tank (1)    Methanol pump (2)    Heat exchanger (3)    Methanol vaporization device (4)    Heat exchanger (5)    Synthesis reactor (6)    Re-boiler (8)    Methanol rectification tower (9)    First condensing heat exchanger (12)    Dimethyl ether pre-rectification tower (14)    Second condensing heat exchanger (17)    Dimethyl ether rectification tower (20)    Third condensing heat exchanger (23)