Scotch Marine fire-tube type boilers from Walker Process Equipment, A Div. of McNish Corp., employ an efficient, forced-draft, dual-fuel burner system that uses digester gas as the primary fuel and can use either natural gas, propane, or fuel oil as the alternate fuel if digester gas pressure is low or not available. They are supplied with a complete electrical control system that includes a modulating control system that reduces the thermal shock on the boiler that otherwise occurs with an on/off control system. They are constructed according to the ASME Boiler and Pressure Vessel Code, Section IV and inspected by an independent, qualified inspector and stamped with the ASME H designation. Each unit is shop-assembled and thoroughly tested prior to shipment. 630-892-7921; www.walker-process.com