A system for transporting and burning under negative pressure in a boiler a raw coke oven gas to produce steam energy. The system has the usual battery of coke ovens and corresponding ascension pipes connected to a collector main. Flushing liquor is sprayed into the hot coke oven gases to effect cooling in the collector main. A transport main delivers the cooled raw coke oven gases and flushing liquor to a burner of a steam producing boiler where the transport main includes a downcomer for separating the raw coke oven gas from the flushing liquor. The coke oven gas is burned in the boiler where a suction fan is provided at the exhaust of the boiler to develop a negative pressure in the system where the boiler has reinforced walls to withstand the negative pressure. A change in negative pressure in the system is detected and monitored by a controller system which varies draw of the suction fan in response to a detected change in negative pressure in the system. The system is readily retrofitted to existing coke ovens and in turn replaces the usual by-products plant. The generated steam may be used in the co-generation of electrical or mechanical energy. The system may be controlled in a manner to minimize and/or eliminate surplus flushing liquors.