Steam power boiler

A method is discussed here, which is based on OSBL conditions. This method can have a profound influence on evaluating project economics and thus determining the project selection. Improper project evaluation could lead to bad investment decisions bad projects are selected and good projects are discarded, which, regrettably, is common in energy optimization evaluations. To avoid the bad investment decisions and determine the true benefits for energy-saving projects, the effects on incremental steam, power, boiler feed water (BFW), and fuel balances must be assessed. A practical example is provided the next to illustrate how this method is applied. 

EXAMPLE 5.1 Dynamics of a Steam-Power Boiler Let us solve the following boiler dynamic response problem. The data for a steam-power boiler installation for a chemical plant are given in Table 5.1. The plant normally runs with a downstream pressure of 165 psia. Determine the unsteady-state response to an opening in the take-off valve that results in a downstream pressure of 150 psia. The boiling relation is given in the steam tables by Keenan and Keyes (1959) as... 

Finally, heat can be turned into work. If our car were steam-powered, for example, we could produce work by exchanging heat with the boiler and the condenser. 

The ASME code provides the basic requirements for over-pressure protection. Section I, Power Boilers, covers fired and unfired steam boilers. All other vessels including exchanger shells and similar pressure containing equipment fall under Section VIII, Pressure Vessels. API RP 520 and lesser API documents supplement the ASME code. These codes specify allowable accumulation, which is the difference between relieving pressure at which the valve reaches full rated flow and set pressure at which the valve starts to open. Accumulation is expressed as percentage of set pressure in Table 1. The articles by Rearick and Isqacs are used throughout this section. 

Relocation of service water pumps and the electrical power distribution system for immunity from steam and boiler feedwater line break... 

Pressure relieving devices in process plants for process and utility steam systems must conform to the requirements of ASME [1] Par. UG-131b. This is not necessarily satisfactory to meet the ASME Power Boiler Code for applications on power generating equipment. 

Safety Valve normally used for steam service, but suitable for gases or vapors. When used in steam generation and process steam service the valves conform to the ASME Power Boiler Code as well as the ASME Pressure Vessel... 

At constant heat flux, CHF occurs at lower steam qualities as pressure rises, thus reinforcing the need to provide the very highest quality of waterside conditions in HP industrial and power boilers. 

Further savings can be made by the use of a suitable blowdown (BD) water flash steam and heat recovery (FSHR) system. Such systems are standard equipment on large power boilers but are less common on smaller plant. However, the FS component (and often the HR component as well) can usually be justified for smaller systems because the capital cost payback of such equipment generally is less than 12 months and such systems continue to save fuel and high-quality water year after year. 

These large industrial manufacturers (paper mills, steel works, oil refineries, petrochemical facilities, etc.) tend to employ either high capacity (200,000-800,000 lb/hr) packaged D-type boilers, or field-erected, two-drum, single gas-pass industrial power boilers, which produce steam at up to 1,800 psig. 

Superheaters and reheaters are tube bundles located in either the boiler furnace section or the convection-pass section. They are designed to increase the temperature of generated steam prior to its being passed to a turbine. Many larger power boiler designs incorporate a steam reheater in addition to one or two banks of superheaters. 

The magnetite film may, under some circumstances, be layered. For example, in power boilers, under conditions of high steaming rate and low steam-water velocity, a secondary film of precipitated particulate iron oxide may form over the original magnetite film. 

Recycled condensate often is of higher quality than FW, although in facilities with extremely long runs of steam and condensate lines, or where amine treatments are not used (e.g., some food processors, hospitals, drug manufacturers, etc.) and in high heat-flux power boiler plants, there is a tendency for the condensate to be contaminated by iron and smaller levels of copper. 

Some of these newer chemistries (those possessing the highest thermal stability) are suitable for application in industrial WT steam generators and power boilers operating at pressures of 1,500 psig and possibly higher. 

These problems are more acute in the power industry, where intermittently operated, peaking steam generators produce and collect significantly more iron oxides than base load boilers. Frequent startups of power boilers are very detrimental to their lifespan. 

A plant is proposing to install a combined heat and power system to supply electrical power and process steam. Power is currently taken from a utility company and steam is generated using on-site boilers. 

It is of special importance to the Lower Dnieper region where Pridneprovsk, Zaporizhia and Krivoi Rog steam power plants, Europe s biggest, are operated alongside with hundreds of smaller plants, cogeneration units and boilers. To abate pollution, one has to find its... 

COMMENTS The effect of increasing the boiler pressure on the quality of the steam at the exit of the turbine can be seen by comparing the two cases. The higher the boiler pressure, the higher the moisture content (or the lower the quality) at the exit of the turbine. Steam with qualities less than 90% at the exit of the turbine, cannot be tolerated in the operation of actual Rankine steam power plants. To increase steam quality at the exit of the turbine, superheating and reheating are used. 

Steam is generated in the boiler of a steam power plant operating on an ideal Rankine cycle at 10 MPa and 500° C at a steady rate of 80 kg/sec. The steam expands in the turbine to a pressure of 7.5 kPa. Determine (1) the quality of the steam at the turbine exit, (2) rate of heat rejection in the condenser, (3) the power delivered by the turbine, and (4) the cycle thermal efficiency (%). 

A steam power plant operates on the Rankine cycle. The steam enters the turbine at 7 MPa and 550°C. It discharges to the condenser at 20 kPa. Determine the quality of the steam at the exit of the turbine, pump work, turbine work, heat added to the boiler, and thermal cycle efficiency. 

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. 

---