Back heating type gasifier

The invention provides a back heating type gasifier. The back heating type gasifier comprises a shell, a refrigerant inlet, a refrigerant outlet, a LNG inlet and a NG outlet, wherein a back heating chamber and a heat exchanging chamber surrounding the back heating chamber are arranged in the shell; the shell also contains a refrigerant isolating chamber arranged between the back heating chamber and the heat exchanging chamber; and communicating channels are respectively arranged between the back heating chamber and the heat exchanging chamber, between the heat exchanging chamber and the refrigerant isolating chamber, and between the refrigerant isolating chamber and the back heating chamber. Through arrangement of the refrigerant isolating chamber, low temperature LNG in the back heating chamber is prevented from directly contacting with the heat exchanging chamber so as to realize prevention of a refrigerant in the heat exchanging chamber from freezing; multi-flow full-countercurrent-flow heat exchanging is