A method of adjusting a duty of heat exchange in a heat integrated distillation column, wherein the heat integrated distillation column comprises: a higher pressure column configured to perform vapor-liquid contact at a relatively higher pressure; a lower pressure column configured to perform vapor-liquid contact at a relatively lower pressure; a compressor configured to pressurize an overhead vapor of the lower pressure column; a first line (L3, L4, L5) for directing a portion of a compressor outlet vapor from the compressor to a column bottom of the higher pressure column via a heat exchange structure, the heat exchange structure being configured to transfer heat from said portion of the compressor outlet vapor to the lower pressure column; a second line (L3, L6) for directing the rest of the compressor outlet vapor from the compressor to the column bottom of the higher pressure column, the second line bypassing the heat exchange structure; and a third line for directing a column bottom liquid of the higher pressure column to a column top of the lower pressure column, wherein the method is for adjusting a duty of heat exchange in said heat exchange structure, and wherein the method comprises: i) totally condensing said portion of the compressor outlet vapor fed to the heat exchange structure in the heat exchange structure; and ii) providing a liquid control valve downstream of the heat exchange structure on the first line, without providing a control valve on a vapor-flowing part of the first and second lines, and adjusting a flow rate of said portion of the compressor outlet vapor flowing into the heat exchange structure by using the liquid control valve, while compensating for a pressure loss needed for the liquid control valve by using a liquid head of a condensate obtained through said condensing, and/or by using pressurization of the condensate by a pump. a higher pressure column configured to perform vapor-liquid contact at a relatively higher pressure; a lower pressure column configured to perform vapor-liquid contact at a relatively lower pressure; a compressor configured to pressurize an overhead vapor of the lower pressure column; a first line (L3, L4, L5) for directing a portion of a compressor outlet vapor from the compressor to a column bottom of the higher pressure column via a heat exchange structure, the heat exchange structure being configured to transfer heat from said portion of the compressor outlet vapor to the lower pressure column; a second line (L3, L6) for directing the rest of the compressor outlet vapor from the compressor to the column bottom of the higher pressure column, the second line bypassing the heat exchange structure; and a third line for directing a column bottom liquid of the higher pressure column to a column top of the lower pressure column, wherein the method is for adjusting a duty of heat exchange in said heat exchange structure, and wherein the method comprises: i) totally condensing said portion of the compressor outlet vapor fed to the heat exchange structure in the heat exchange structure; and ii) providing a liquid control valve downstream of the heat exchange structure on the first line, without providing a control valve on a vapor-flowing part of the first and second lines, and adjusting a flow rate of said portion of the compressor outlet vapor flowing into the heat exchange structure by using the liquid control valve, while compensating for a pressure loss needed for the liquid control valve by using a liquid head of a condensate obtained through said condensing, and/or by using pressurization of the condensate by a pump. i) totally condensing said portion of the compressor outlet vapor fed to the heat exchange structure in the heat exchange structure; and ii) providing a liquid control valve downstream of the heat exchange structure on the first line, without providing a control valve on a vapor-flowing part of the first and second lines, and adjusting a flow rate of said portion of the compressor outlet vapor flowing into the heat exchange structure by using the liquid control valve, while compensating for a pressure loss needed for the liquid control valve by using a liquid head of a condensate obtained through said condensing, and/or by using pressurization of the condensate by a pump.