Tunnelflow" - Gasinlet Tubesheet Design An appropriate Gasinlet Tubesheet design is necessary due to the following two requirements: The high pressure on waterside (up to 150 bar g) calls for a thick tubesheet. The high gasinlet temperature and the high gasside heat transfer coefficient calls for a thin tubesheet in order to keep its metal temperature low. A thick tubesheet is impracticable because metal temperature of the tubesheet would be too high due to heat transport from the gas into the tubesheet. The patented BORSIG linear quencher (BLQ) consists of a number of linearly arranged double pipe elements of which each is directly coupled to one of the furnace radiant coil outlets. The process effluent from each single radiant coil is quenched individually in its own double pipe element. A common downcomer header distributes uniformly the circulating boiler water coming from the steam drum to each of the “Turboflow” inlet chambers. A riser header is collecting the steam/water mixture from the upper outlet chambers.