Technology & Engineering
Feedwater Heater
A feedwater heater is a device used in power plants to preheat water before it enters the boiler. This helps to improve the overall efficiency of the power plant by reducing the amount of fuel needed to produce steam. The heater typically uses steam extracted from the turbine to heat the feedwater, recovering some of the heat that would otherwise be wasted.
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5 Key excerpts on "Feedwater Heater"
eBook - PDFSustainable Utility Systems
Modelling and Optimisation
- Petar Sabev Varbanov, Jiří Škorpík, Jiří Pospíšil, Jiří Jaromír Klemeš(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
5 Steam generators This chapter provides an overview of the main concepts in steam generation and gen-erators, providing links to specialised sources for obtaining more details. That is fol-lowed by an overview of Boiler Feed Water (BFW) – the need for treatment, stages of treatment, then by a discussion of boiler blowdown. The chapter is completed by a description of the steam generator models for utility network optimisation. Steam generators are mostly referred to as “ steam boilers ” in the industry (Ganapathy, 2017). The primary function of the boiler is to generate steam. In industry, the main use of the steam is for process heating and any steam generated at a pressure higher than the required use can be expanded via steam turbines, to cogenerate power. A boiler consists of two principal parts: – The furnace, where heat is generated, usually by burning a fuel – The boiler chamber/drum in which the heat is supplied to the water stream to become steam. Steam boilers can be of various sizes, which depend on the desired capacity and the type. Steam generators can be implemented as single devices, where one pos-sible design is, as described previously, a furnace with high-temperature-resistant tubes built into the facility. Sometimes, a heat exchanger used for process cooling can play the role of a steam generator – provided that the process cooling demand is at sufficiently high temperature (Kleme š et al., 2018). A steam boiler converts a particular heat input – from a hot stream or from combusting fuel, into steam at the specified pressure and temperature. In some cases, for lower temperature ap-plications such as in the food industry, hot water is used instead of steam. The commonly used fuels in the industry are fossil fuels as coal, fuel oil and natural gas, as well as biomass – mostly wood.
eBook - PDF- Carey Merritt(Author)
- 2022(Publication Date)
- Wiley(Publisher)
Process Steam Systems: A Practical Guide for Operators, Maintainers, Designers, and Educators, Second Edition. Carey Merritt. © 2023 John Wiley & Sons, Inc. Published 2023 by John Wiley & Sons, Inc. 11 THE FEED WATER SYSTEM A boiler feed water system receives the condensate from the condensate system and stores the condensate in a feed water tank. Once the condensate reaches the feed water tank it becomes feed water. The feed water system prepares the water for reintroduction into the boiler. This preparation includes, collection, deaeration, and pumping the water to the boiler. A flow diagram for a typical feed water system is shown below in Figure 11.1. Feed water requirement is defined as follows: Boiler feed water require- ment = boiler evaporation rate + boiler blowdown rate + any system steam leaks. Feed water flow = fresh makeup water rate + return condensate rate. Therefore boiler evaporation + blowdown rate + steam leaks must equal condensate return and fresh makeup rate. A water balance in the steam system would show this to be true. A steam system with “60% returns” would mean that the feed water would contain 40% makeup water and 60% condensate return water. Steam system designers should always perform a water balance early in the design process. Pumps, water treatment equipment, condensate, and feed water tank sizes can be accurately determined once the water balance is determined. More on this type of analysis in Chapter 12. FEED WATER DEAERATION Prior to discussing feed water system design, one should understand the principles of deaeration. Mechanical deaeration is the process of mechanically removing all dis- solved gases from the feed water and is an integral part of any modern steam boiler protection program. Deaeration, coupled with other aspects of water treatment, provides the best and highest-quality feed water for boiler use. The purposes of deaeration are
eBook - PDFIndustrial Steam Systems
Fundamentals and Best Design Practices
- Mojtaba Sabet(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
In most operations, oxygen scavenger 34 Industrial Steam Systems chemicals are added to the tank to further reduce the oxygen level. Of course, the added chemicals settle inside the boiler chamber and require additional boiler blowoff that in turn increases the boiler makeup water. A heating tank feed water package is simple and inexpensive, but it has the following disadvantages: 1. Inadequate removal of CO 2 and O 2 to prevent boiler internal corrosion. 2. Heat and water losses due to the tank atmospheric pressure (vented), especially if there is a high-temperature condensate return that flashes to steam and discharges through the vent. 3. Lack of ability to control the water temperature evenly inside the tank. This can cause feeding the boiler with water that is not hot enough to minimize boiler thermal shock. Boiler thermal shock can compromise its integrity and shorten its life cycle. A heating tank feed water package includes the following components. Storage Tank An atmospheric tank sized for a minimum of 10 min of water storage based on the boiler output steam flow rate plus a 25% safety factor. The safety fac-tor is to account for the possible simultaneous pumped condensate returns. The tank is elevated and installed on a structural stand to provide adequate suction head for the boiler feed water pump to prevent cavitation. The tank is insulated to conserve heat and internally lined to minimize corrosion. There are connections on the tank for maintaining tank atmospheric pressure by venting, receiving condensate, steam feed for water heating (if steam is used), makeup water supply, drain, overflow, boiler feed water pump outlet, and installing instrumentations and control devices. Water Heater Usually a steam sparger is used for heating the water inside the storage tank. A temperature control valve on the steam supply line maintains the water temperature at approximately 212°F (100°C).
eBook - PDFCombined Heating, Cooling & Power Handbook
Technologies & Applications, Second Edition
- Neil Petchers(Author)
- 2020(Publication Date)
- River Publishers(Publisher)
Finally, after all of the water has evaporated to steam, the volume continues to increase and the temperature rises — this is superheating . The heat transfer sections of a conventional steam generator may be divided into three functional compo-nents: an economizer, which uses recovered energy to heat the feedwater nearly to its boiling point, an evapora-tor, and a superheater. Very large boilers may use several stages of superheaters, evaporators, and economizers to maximize the thermal efficiency of boiler and power gen-erating systems. In the basic large boiler system, saturated or super-heated steam at a set pressure and temperature exits the boiler into a central steam header and then passes to vari-ous branches in the distribution system. Steam pressure may be reduced at local pressure reducing stations to meet the requirements of various loads. At the point of use, the steam condenses to liquid water with a trans-fer of heat to the designated load. Liquid condensate is returned to the boiler through the deaerator to start the process over again. Boiler feedwater may consist of return condensate, fresh makeup water or a mixture of both. Where near-ly all condensate is returned, only a small percentage of makeup water is required. But in systems that include large steam and condensate losses, makeup may comprise a high proportion of boiler feedwater. Impurities that contribute to scaling and fouling of boiler surfaces are removed through treatment of boiler feedwater and through a blowdown process. Impurities are broadly classified as suspended or dissolved organic and inorganic matter and dissolved gases. The concentra-tion of impurities is typically expressed in terms of the parts by weight of the constituent per million parts of water (ppm). Water treatment may include filtering to remove suspended solids and chemical treatment for removal of hardness, or dissolved minerals.
eBook - PDF- DENNIS A SNOW(Author)
- 2013(Publication Date)
- Newnes(Publisher)
On top of this capacity a volume has to be allowed for condense returns when the system starts in order to prevent wastage of heat and water. As steam capacities increase, the feed tank becomes correspondingly larger, and it may be considered that on steam outputs in excess of 20000 kg/h a duplex treatment plant should be installed in order to keep the feed tank to a reasonable size. In areas where the water demand of the plant may exceed the supply capacity of the local mains it will be necessary to install additional storage tanks. It is likely that if the local supply is subject to low flow rates additional storage is already available for services such as fire protection. Feedwater to the boiler should not be cold, as this can cause harmful thermal stresses to the boiler. A minimum feedwater temperature of 70-80 ü C should be designed into the system. This increased temperature has the added advantage that it accelerates some water-treatment reactions and also helps to remove oxygen and other gases from the feedwater. Once the system is working, this higher temperature may be achieved from the condense returns, but this condition is not effective until the plant has been running for some time. A tank heating system should therefore be installed. This is best achieved by direct steam injection into the feed tank. Steam is Blowdown requirements, control and tanks 7/19 1177 W/m 2 12 600 W/m 2 r- Bare tank 50 mm lagging (90% eff.) 91 W/m 2 905 W/m 2 59 W/m 2 588 W/m 2 Figure 7.10 Heat losses from a feedwater tank operating at 93°C with ambient 21 °C taken from the boiler and reduced in pressure to 1 - 2 bar to reduce noise in the tank. Passing through a thermostatic control valve, the steam mixes with the water in the tank through a sparge pipe or steam nozzle. With watertube boilers economizers are normally used, therefore the situation of cold feed to the boiler would not apply.
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