Steam-Generation System Boilers

The production of steam is very important to the operation of an industrial facility. Steam is used in a variety of operations, including heating and temperature control, steam turbines, steam tracing, heat exchangers, reboilers, stripping, and distillation. The energy in steam can easily be 

A steam-generation system is designed to safely return cooled condensate to the boiler. A device called a steam trap is used to collect and transfer this material. Low points in the steam system are used to capture cooled condensate before it can damage the piping or equipment. Water can expand to many times its original volume when vaporized, so the condensate return header is a 

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The boiler steam generation system primarily covers the boiler itself, the boiler surfaces (the primary heat-transfer and steam-generating surfaces within the boiler proper), and all necessary appurtenances. 

Application Challenges Eor this steam system, a revamp project requires 40 klb/h of additional HP steam and the limits of steam generation from boilers 1 and 2 are 160 and 140 klb/h, respectively. Since the current loading of both boilers 1 and 2 are at 108 klb/h respectively. Naturally, the hrst 32 klb/h HP steam demand will be provided from boiler 2 since it is more efficient than boiler 1. Thus, the marginal price for 32 t/h from boiler 2 is 11.3/klb, while the last 8 t/h to be made from boiler 2 will be priced at 12.5/klb. 

Process Leaks Process leaks can occur with varying frequency. Instrumentation must be provided to monitor condensate quality to prevent damage to the boiler. Normal practice is to sewer condensate upon evidence of contamination until it is determined that the contamination is not severe enough to cause problems in the steam generation system. Procedures must be provided to identify and isolate causes of contamination rapidly. Provisions for segregating the system into small segments should be provided. 

Boilers—devices primarily designed to boil water and generate steam for industrial applications. Boilers are classified as either water tube or fire tube. Steam generation systems produce high-, medium-, and low-pressure steam for industrial use. 

A Steam generator or boiler is used by industry to boil water and produce high-, medium-, or low-pressure steam. The symbol for a boiler closely resembles that for a large water-tube boiler. Boilers are composed of an upper steam-generating drum, a lower mud drum, downcomer tubes, riser tubes, steam-generating tubes, an economizer section, a water make-up system, a stack, a fan, and burners. All of these devices are neatly enclosed inside a refractory-lined shell designed to reflect heat back into the furnace. 

Steam-generation system—a complex arrangement of boiler systems designed to convert water to steam. These include pump-around systems, advanced process control systems and instruments, fuel systems, and compressor systems. 

The heart of a steam-generation system is the boiler that produces steam for the high, medium, and low steam systems. A condensate return system captures and returns condensate to the boiler. Figure 9-11 shows how each part in the steam generation system works. 

A steam-generation system is a complex arrangement of equipment and subsystems designed to produce clean, dry steam for industrial applications. The industrial steam produced from boilers... 

The wastewater from a hydrogen plant typically consists of only the blowdovm from the boiler system. The boiler feedwater that feeds the steam generation system has small amounts of impurities such as sodium, chlorides, silica, and organic carbons. These impurities will accumulate within the boiler system and create sludge, scaling of the boiler tubes, and possible carryover of solids into the process steam. Blowdown of the boiler water is performed to prevent these issues from affecting the operation of the steam system. The blowdown is typically sent to the sewer or the on-site waste treatment plant for treatment and disposal. 

Water Treatment. Water and steam chemistry must be rigorously controlled to prevent deposition of impurities and corrosion of the steam cycle. Deposition on boiler tubing walls reduces heat transfer and can lead to overheating, creep, and eventual failure. Additionally, corrosion can develop under the deposits and lead to failure. If steam is used for chemical processes or as a heat-transfer medium for food and pharmaceutical preparation there are limitations on the additives that may be used. Steam purity requirements set the allowable impurity concentrations for the rest of most cycles. Once contaminants enter the steam, there is no practical way to remove them. Thus all purification must be carried out in the boiler or preboiler part of the cycle. The principal exception is in the case of nuclear steam generators, which require very pure water. These tend to provide steam that is considerably lower in most impurities than the turbine requires. A variety of water treatments are summarized in Table 5. Although the subtieties of water treatment in steam systems are beyond the scope of this article, uses of various additives maybe summarized as follows ... 

Boiler Design Issues Boiler design involves the interaction of many variables water-steam circulation, fuel characteristics, firing systems and heat input, and heat transfer. The furnace enclosure is one of the most critical components of a steam generator and must be conservatively designed to assure high boiler availability. The furnace... 

Steam-Generator Circulation System Circulation systems for utility application are generally classified as natural circulation and forced or pump-assisted circulation in drum-type boilers, and as once-through now in subcritical- and supercriticaf-pressure boilers. The... 

Process Steam Generation. Steam generated in the process sections of the plant may be at the highest plant pressure level or an intermediate level. Also, the process area may have fired boilers, waste heat boilers, or both. There may be crossties between utility and process generated steam levels. Enough controls must be provided to balance far-ranging steam systems and protect the most critical units in the event of boiler feedwater shortage situations. 

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