Feed water, heaters

In subsequent years, Savery made important improvements that benefited future steam inventions. In June 1699 he demonstrated to the Royal Society a pump with two receivers, each with a separate, hand-controlled steam supply. This ensured improved continuity of operation, allowing one receiver tn operate in its vacuum stage and the other under steam pressure. In 1701, he added two more critical steps a second boiler, avoiding the need to shut down the fire and pump, between stages and he replaced the two interconnected steam cocks with a single valve, run with a manually operated long lever. This may have been the inspiration for the modern slide valve and his inventiveness created, in effect, the world s first feed-water heater. 

Determine the efficiency and power output of a regenerative Rankine cycle using steam as the working fluid and a condenser pressure of 80 kPa. The boiler pressure is 3 MPa. The steam leaves the boiler at 400° C. The mass rate of steam flow is 1 kg/sec. The pump efficiency is 85% and the turbine efficiency is 88%. After expansion in the high-pressure turbine to 400 kPa, some of the steam is extracted from the turbine exit for the purpose of heating the feed-water in an open feed-water heater, the rest of the steam is reheated to 400°C and then expanded in the low-pressure turbine to the condenser. The water leaves the open feed-water heater at 400 kPa as saturated liquid. Determine the steam fraction extracted from the turbine exit, cycle efficiency, and net power output of the cycle. 

Take two pumps, a boiler, a turbine, a reheater, another turbine, a splitter, a mixing chamber (open feed-water heater), and a condenser from the inventory shop and connect the devices to form the regenerating Rankine cycle. Switch to analysis mode. 

Plot the sensitivity diagram of cycle efficiency versus open feed-water heater temperature. 

Consider a steam power plant operating on the ideal regenerating Rankine cycle 1 kg/sec of steam flow enters the turbine at 15 MPa and 600°C and is condensed in the condenser at lOkPa. Some steam leaves the high-pressure turbine at 1.2 MPa and enters the open feed-water heater. If the steam at the exit of the open feed-water heater is saturated liquid, determine (1) the fraction of steam not extracted from the high-pressure turbine, (2) the rate of heat added to the boiler, (3) the rate of heat removed from the condenser, (4) the turbine power produced by the high-pressure turbine, (5) the turbine power produced by the low-pressure turbine, (6) the power required by the low-pressure pump, (7) the power required by the high-pressure pump, and (8) the thermal cycle efficiency. 

Determine the power required by the compressor, power required by pumps 1 and 2, power produced by turbines 1, 2, and 3, rate of heat added by the nuclear reactor, net power produced by the Brayton gas turbine plant, net power produced by the Rankine plant, rate of heat removed by coolers 1 and 2, rate of heat exchanged in the heat exchanger, rate of heat added in the gas burner, mass rate flow of helium in the Brayton cycle, mass rate flow of steam extracted to the feed-water heater (mixing chamber), cycle efficiency of the Brayton plant, cycle efficiency of the Rankine plant, and cycle efficiency of the combined Brayton-Rankine plant. 

Figure 2. Useful energy costs Ag of bleed steam for feed-water heaters.

This result must of course be correted for small values of XQpt using the correction factor mentioned above. For feedwater heaters, a similar result is obtained by expanding the logarithm in Eqn. (15) to obtain a value of Oy = (y-l) /2y which needs another correction factor to conform to Eqn. (15) exactly. This merely introduces a factor of two into Eqn. (A2) so that for feed-water heaters, the corresponding basic results is... 

Hendrix, W. A., "Essergy Optimization of Regenerative Feed-water Heaters," Master s Thesis, GA Inst, of Technology, Atlanta, GA (1978). 

In this ideal regenerative Rankine cycle, the steam extracted from the turbine heats the water from the condenser, and the water is pumped to the boiler. Sometimes, this occurs in several stages. The condensate from the feed water heaters is throttled to the next heater at lower pressure. The condensate of the final heater is flashed into the condenser... 

As shown in Figure 11.21, the power island of an IGCC plant consisted of GTs that use syngas as fuel, an HRSG, and steam turbines. Additional condensers, feed water heaters, and compressors are also essential parts of the steam power cycles. 

Feed-water Heaters.—Types include the open heater (Cochrane, Webster) in which the exhaust steam and water mix, and the closed heater, in which the water circulates in tubes surrounded by exhaust steam. Open heaters give slightly higher feed temperatures at the same back pressure, or slightly less back pressure at the same feed temperature. Filters, separators, etc., are provided to remove oil from the exhaust. The open heater forms a convenient receptacle for various drips, for the automatic introduction of any cold water make-up supply and for certain forms of feed-water treatment and purification. It may be of the thoroughfare type in which all exhaust steam in the pipe passes through the heater, or of the draw in type in which a branch from the auxiliary exhaust leads to the heater as a dead end. Open heaters must be located on the suction side of the feed pump and above (preferably 3 ft. or more above) the level of the feed-pump suction valves. 

Economizer.—The economizer is a feed-water heater using boiler flue gases as the heating agent. It usually consists of a single unit for an entire row of boilers, with a gas bypass to the stack. The surface is made up of vertical cast-iron tubes, 4 in. in diameter and 10 or 12 ft. long, through which the water rises. The outsides of the tubes are cleaned of soot by power-operated scrapers. Economizers obstruct the draft and often necessitate the use of fans. 

Condensers.—From a thermal standpoint, condensers may be classified as mixing (horizontal independent jet, injector or barometric) and non-mixing (surface) types.. The equations above given for feed-water heaters will apply as an error on the safe side, x may be taken as 1.0. The value of ti is determined by the available supply of cooling water in this latitude under summer conditions, it is rarely below 70°. That of to will be in surface condensers 6 to 10° below tj and that of t2 the same amount below U- The value of to determines the best possible vacuum. Orrok gives k = SfiOr VF, for clean copper tubes, where V = water velocity in tubes, feet per second, r = ratio of partial pressure of steam to total pressure in the condenser. If condensers and vacuum pumps are tight, r == 0.95. 

The D head uses a special closure similar to the breech of an artillery piece, with application to high-pressure feed-water heaters in power plants and some high-pressure chemical processes. 

Often a boiler has to be designed for dual fuel, e.g., natural gas and heayyipjOL. Sulfur content may also v y. Ilf cH applications it may be justifiable to have the feed water temperature made variable by means of an adjustable feed water heater. Bleed or back pressure steam can be used if available. Thus, optimum use can be made of the installed economizer surface. 

ASME PART PFH SECTION I - Requirements for feed water heaters. 

CLOSED FEED WATER HEATER - An indirect-contact feed water heater. Steam and water are separated by tubes. 

Steam enters the high pressure cylinder and subsequently passes through the moisture separators and reheaters before entering low pressure cylinders. The steam then exhausts to a condenser under vacuum. The condensed steam is extracted from condenser by condensate extraction pumps and the condensate passes through feed water heaters to deaerator. Boiler feed pumps take suction from deaerator and pump feed water via high pressure feed water heaters into steam generators. 

The feed water system consists of main water pumps, auxiliary feed water pumps, feed water heaters, etc. The feed water heaters consist of a low pressure feed water heater, a dearator, and two stage high pressure feed water heaters which raise the temperature of feed water to 185°C. 

A tud building contains a turbine system, an electric generating stem, a condenser, a feed water system and connecting piping. All systems are non-nuclear grade. The feed water stem has three low pressure feed wat heaters and one high pressure feed water heater, and has two main feed water pumps. 

---