Abstract: A flameless nitrogen liquid to gas converter for providing high pressure nitrogen gas to treat oil and gas wells. A diesel engine prime mover drives hydraulic pumps and motors to pressurize nitrogen and actuate a closed-loop water system and a series of heat exchangers. The closed-loop water system provides heat for converting the liquid nitrogen to gaseous nitrogen which is obtained from the engine jacket water, the engine exhaust and the hydraulic oil from the hydraulic pumps and motors. Additional heat can be obtained from the hydraulic oil system by increasing the hydraulic system pressure with an hydraulic pressure control valve. At least one of the hydraulic pumps and its driven hydraulic motor is in an hydraulic circuit which includes variable means for increasing the pressure in the hydraulic circuit, hydraulic oil-water heat exchanger and an hydraulic oil reservoir. Hydraulic fluid from the other pumps and motors is transmitted through the hydraulic oil-water heat exchanger.