Abstract: A heat recovery steam generator (HRSG) (A) has a casing (2) and several heat exchangers in the casing. Some of those heat exchangers (12,16) take the form of coils (18) having multiple lower headers (36) into which the lower ends of tubes (18) open. The tubes (18) and headers (36) hold or may hold water and need to be drained from time to time. To this end, the heat ex changer (12,16) has a drain system (20) provided with drain pipes (40) that are connected to the lower headers (36) and contain check valves (48) that permit the water to flow away from the headers (36), but not into them. The drain pipes (40) lead to and open into a drain manifold (46). The drain pipes (40), check valves (48) and drain manifold (46) are assembled in a shop along with the coil (18) and, when the HRSG (A) is assembled in the field, lie within the interior of the casing (2).

Abstract: A blowoff tank (B) for receiving blowdown, blowoff, and drain water from an HRSG (C) or other type of boiler, so as to lower the temperature of that water enough to enable it to be discharged into a sewer system, includes a generally cylindrical vessel (50) and inlet pipes (60) through which the blowdown, blowoff, and drain water is introduced into the vessel. Each pipe has a radial segment (62) that passes through the sidewall (52) of the vessel, a generally vertical segment (64) that extends upwardly within the vessel, and a tangential segment (68) that opens into the vessel. The radial segment contains a small drain aperture (74). The tank also has a cooling line (90) through which cooling water is introduced into the vessel to lower the temperature of the blowdown, blowoff, and drain water in the vessel and a drain line (86) that drains the mixture of cooling water and blowdown, blowoff, and drain water from the vessel, but never exceeds the elevation of the apertures in the inlet pipes.

Abstract: A feedwater heater (14) in a heat recovery steam generator (A,B) lies within a flow of hot exhaust gas. The feedwater heater (14) converts subcooled feedwater into saturated feedwater water, the temperature of which is only lightly above the acid dew point temperature of the exhaust gas so that corrosive acids do not condense on coils (18) of the feedwater heater (14). Yet the temperature of the saturated feedwater lies significantly below the temperature of the exhaust gas at the coils (18), so that the coils (18) operate efficiently and require minimal surface area. Pumps (26, 28, 30) elevate the pressure of the saturated feedwater and direct it into an economizer (64, 90) where, owing to the increase in pressure, the water is again subcooled. The economizer (64, 90) elevates the temperature still further and delivers the higher pressure feedwater to evaporators (34, 70, 78) that convert it into saturated steam that flows on to the superheaters (50, 78, 84).

Abstract: A feedwater heater (10) for a steam generator communicating feedwater through an external heat exchanger (12), a deaerator (14) that allows the use of carbon steel feedwater tubes, a first heater (16), an evaporator section (18) and steam drum (17) for communicating a portion of the feedwater in the form of steam to the deaerator (14), and a second heater (20).

Abstract: A blowoff tank (B) for receiving blow-down, blowoff, and drain water from an HRSG (C) or other type of boiler, so as to lower the temperature of that water enough to enable it to be discharged into a sewer system, includes a generally cylindrical vessel (50) and inlet pipes (60) through which the blowdown, blowoff, and drain water is introduced into the vessel. Each pipe has a radial segment (62) that passes through the sidewall (52) of the vessel, a generally vertical segment (64) that extends upwardly within the vessel, and a tangential segment (68) that opens into the vessel. The radial segment contains a small drain aperture (74). The tank also has a cooling line (90) through which cooling water is introduced into the vessel to lower the temperature of the blowdown, blowoff, and drain water in the vessel and a drain line (86) that drains the mixture of cooling water and blowdown, blowoff, and drain water from the vessel, but never exceeds the elevation of the apertures in the inlet pipes.

Abstract: A feedwater heater for an HRSG is provided with a monitoring unit for detecting the presence of condensation in the feedwater heater. The monitoring unit includes a dielectric band around one of the tubes of the feedwater heater near the location where the feedwater is directed into the heater and a conductive band located around the dielectric band. The unit also includes a conductivity sensor installed between a ground on the feedwater heater and the conductive element. Hot gases containing moisture pass through the feedwater heater, and if the temperature of surfaces in the region of the tube around which the dielectric and conductive bands extend drops below the dew point of the gas, an electrically conductive condensate will appear those surfaces and on the tube and will flow over the dielectric band, completing an electric circuit between the tube and the conductive band. The conductivity sensor detects this and hence detects the presence of the condensation.

Abstract: An evaporator in a steam generator extracts heat from high temperature gases to convert heated water into saturated steam. The evaporator includes two sections—a once-through section and a circulation section, both of which include tubes located in the flow of hot gases. Heated water flows through the tubes of the once-through section at a rate sufficient to maintain the interiors of its tube fully wetted while enabling steam to develop in that water, with the steam having a quality of at least 20%. The circulation section includes a drum that is connected to the tubes of that section such that water from the drum circulates through the tubes and then back to the drum, with the circulation being such that the water in the tubes of the circulation section keeps the tubes fully wetted while steam develops in that water. The water from the tubes of the once-through section discharges into the drum as does the water circulating back from the tubes of the circulation section.

Abstract: A feedwater heater for a steam generator or heat recovery boiler or waste heat boiler through which hot gases pass includes two sections which are located side by side so that the temperature of the hot gases at the upstream face of each section is essentially the same. The feedwater flows through a heat exchanger before entering the first section, and here it is heated by water flowing from the upstream face of the first section to the downstream face of the second section. The arrangement is such that all tubes in the two sections remain above the dew point of the hot gases, so that water does not condense on the tubes and unite with oxides of sulfur to form sulfuric acid which will corrode the tubes, yet substantial temperature differentials exist between the water in the sections and hot gases as the gases pass through the sections.