Basics of boiler and hrsg design pdf download

Books by Brad Buecker. No other book explains the fundame An excellent primer for power plant professionals who have to wear many hats and need a practical explanation of the design and basic operation of conventional steam generating boilers and HRSGs without having to wade through technical material. Goodreads helps you keep track of books you want to bradd.

Lists with This Book. Ashish Paladiya added it Apr 08, This book is not yet featured on Listopia. Return to Book Page. Rusdianto Sartono is currently reading it Nov 01, Buecker uses anecdotes and humor to liven up what would otherwise be considered a dry subject.

Visit our Beautiful Books page and find lovely books for kids, photography lovers and more. Just a moment while we sign you in to your Goodreads account. Book ratings by Goodreads. Ada marked it as to-read Jun 21, We use cookies to give you the best possible experience. Refresh and try again. Disadvantages of fluidized bed combustion Like all technologies, fluidized bed combustion is not foolproof Of prime concern is the corrosive character of the ash, especially when it is accelerated to high speed in the cyclone.

Also, part of the furnace is lined with refractory-a material susceptible to thermal stress-that may spall off if the unit is frequently cycled. Thus, CFBs operate best in base-mode fashion. Fuel switching, while eas- ier to do than in other types of boilers, may be complicated if the moisture content changes drastically. Emissions regulations could present challenges for CFBs as well as other coal- fired boilers.

A CFB does not remove mercury, for example, and so this pollutant has to be controlled by backend methods. Control of particulate matter less than 2. Emissions limits of 0. However, in-furnace removal of most of the NOX and so2 would greatly reduce load on any backend pollution control equipment, thus reducing capital and operating costs. CFBs already compare favorably with pul- verized-coal fired units in terms of capital cost.

CFBs' versatility is illustrated in the Foster Wheeler advanced circulating flu- idized bed plant, in which a pressurized circulating fluidized bed not only gener- ates steam for power production but also generates a syngas that can be fed to a combustion turbine or co-generation process.

Also under consideration are once- through supercritical CFBs. Like their sub-critical counterparts, they could offer a capital cost advantage over pulverized coal units that must be equipped with large, backend pollution control systems. Combined-cycle power generation and heat recovery steam generators A significant amount of electricity is now generated using simple-cycle and combined-cycle natural gas-fired occasionally oil-fired power plants. The basic outline of a simple-cycle gas turbine is shown in Figure This process is tech- nically referred to as the Brayton cycle.

Compressed air produced in the front stage of the unit is fed to the combustor, where the burning fuel produces expanding gases that drive a vaned turbine, which, like a conventional steam turbine, spins a magnet inside a coiled generator to produce power. The process is not unlike that of a jet engine except that the turbine produces "shaft work" rather than thrust. A primary advantage of simple-cycle combustion turbines is that these units can be started quickly and are ideal for peak load situations.

Also, the compressor consumes a great deal of energy. A very considerable efficiency improvement is possible by using the exhaust gas from the combustion turbine to heat a steam generator. The key component in a combined-cycle plant is the heat recovery steam gen- erator HRSG. The primary modes of heating in HRSGs are convection and conduction, so the physical layout of waterwall, superheater, and reheater tubes is different than in conventional boilers.

Figure shows the general outline of the most common HRSG design, where the boiler tubes are vertically oriented and the gas turbine exhaust passes through in a horizontal direction. Some HRSGs are single-pressure units, but much more common are multi- ple-pressure systems, as they offer improved efficiency.

Figure illustrates a triple-pressure HRSG-several aspects of this unit stand out. First is the configu- ration of the circuits within the HRSG. Those in the hottest zone are the high- pressure HP reheater, superheater, and evaporator boiler. These are followed by the intermediate-pressure IP and low-pressure LP circuits. Each evaporator is set up in a natural circulation, drum-type arrangement, and the HP and LP cir- cuits generate steam for power production. The deaerator is incorporated directly into the LP circuit to remove dissolved gases.

Combined-cycle power plants may be equipped with auxiliary, natural gas- fired duct burners to increase the heat flow to the HRSG, but this has not been universally adopted.

In general-and especially in HRSGs without supplemental burners-heat fluxes are lower than in a conventional boiler, so the design often incorporates finned tubes to assist with heat transfer.

The drawback to finned tub- ing is that the tubes are difficult to remove for deposit sampling or other mainte- nance activities. Two important heat transfer criteria stand out regarding HRSGs-approach temperature and pinch-point temperature. The approach temperature is the difference in. The "Newer" Technolgies I When factors such as economizer size, efficiency, and equipment costs are taken into account, a properly designed economizer will bring the feed- water temperature to within 9oF to 22oF 5 to 12T of the boiler water saturation temperature.

Tighter approach temperatures would make the size and cost of the economizer prohibitively large. In addition, narrow approach temperatures can cause steaming in the economizer. Steaming may cause water hammer and fluctu- ations in drum level.

The pinch-point temperature is the difference between evaporator steam out- let temperature and the exhaust gas temperature at that physical location in the HRSG. Figure illustrates by diagram the approach and pinch-point temperature rela- tion for a single-pressure HRSG.

Lower pinch-point temperatures require larger. I Approach I em perature. Many factors can influence the efficiency of a combined-cycle plant, and a discussion of most of these factors is beyond the scope of this book. See ref- erence section at end of book. One concept that stands out, however, is that in a combined-cycle plant, the efficiencies of two systems the gas turbine and the HRSG influence the overall efficiency of the unit.

In some cases, an efficiency decline in one positively affects the other! For example, a loss of efficiency in the gas turbine would increase the exhaust temperature, causing a rise in steam pro- duction in the HRSG. In general, efficiency losses in the gas turbine negatively affect overall performance, and it is best to design and operate the system with the gas turbine at maximum efficiency. Figure shows the output and efficiency of a combined-cycle unit as HRSG back-pressure increases.

Clearly illustrated is the decline in gas turbine output and efficiency. Increased back-pressure improves heat transfer in the HRSG, but the loss of efficiency in the gas turbine more than off-. GT Output and Efficiency. Not all HRSGs are of the vertical-tube drum design. These are not as common as the vertical-tube type. One issue of primary concern in HRSGs is flow-assisted-corrosion. This cor- rosion mechanism, influenced by water chemistry, flow patterns, and temperature,.

Appendix provides addi- tional details regarding this phenomenon. Alternate fuel boilers and stoker-fired units Stoker-fired boilers could have logically been introduced in chapter 1, as stok- er firing has been around for a long time. However, stokers are not common for modern large generator applications, so the discussion has been delayed until now.

Stokers are still popular for alternate fuel firing including biomass and refuse- derived fuel. Stokers resemble other steam-generating units, with the notable exception that the fuel combusts on or just above a mechanical grate. Primary air feed for a stoker comes from below the grate, and fuel may be fed below the grate under- feed or above the grate overfeed.

Two of the most popular stoker types are the overfeed traveling grate stoker and the overfeed spreader stoker depicted in Figs. A discussion of how stokers operate with coal offers a good introduction into the topic of alternate fuel firing. Consider first Figure , the outline of a traveling grate stoker. Coal is fed at the leading end of the stoker grate. Primary air feed comes from below the grate with some overfire air above the grate for NOx control.

The underfire air prevents the grate from overheating. As the grate traverses the furnace, the coal combusts, being reduced to ash by the time it reaches the opposite side of the furnace. A vari- able underfire airflow pattern is common to provide more air to the coal at the entry point and less as the coal loses combustible material.

Figure shows a spreader stoker unit with a vibrating grate. In these boil- ers, mechanical spreaders distribute the fuel uniformly over the stoker grate to pro- vide a more even combustion pattern. The vibration causes the fuel to flow to one end of the grate. With a properly designed furnace, the fuel is converted almost entirely to ash by the time it reaches the edge of the grate and falls into the ash col- lection system.

In the spreader stoker, where the fuel is thrown onto the grate, the smaller coal particles tend to fluidize and burn a short distance above the grate.

Larger particles fall onto the grate and combust there. Difficulties that must be overcome with stoker units include grate overheat- ing and ash clinkering. Grate cooling may be accomplished in several ways. Air- cooled grates use the flow of underfrre air to protect the equipment. Vibrating stoker grates may be water cooled, with cooling tubes connected to the waterwall network.

Ash that fuses together in large chunks is known by the term "clinkers. Uniform fuel distribution is a key in preventing clinker formation. Stokers are not popular for new utility coal units, as the more modern tech- niques of pulverized coal firing and fluidized-bed combustion offer better effi- ciency. However, stokers are one of the viable methods to combust fuels that are difficult or impossible to reduce in size.

These include biomass and refuse-derived fuel RDF. Biomass includes wood, bark, agricultural by-products such as corn stalks, and even more exotic materials like bamboo stalks and rice hulls. A very interesting fact about biomass is that growing plants absorb almost as much carbon dioxide as they give off during combustion. This offers potential in the fight to stabilize C02 em1sswns. RDF-powered generation and co-generation offer methods to dispose of waste other than by landfilling.

RDF is a difficult material to handle and burn. Fuel quality is quite variable and combustion produces significant chloride con- centrations in the furnace, which can cause serious corrosion in the boiler and boil- er backpass. Techniques to combat corrosion include the use of refractory in high heat areas of the furnace and more exotic alloys for boiler and superheater tube material.

A new process for refuse mass burning that combines aspects of fluidized bed combustion and stokers is shown in Figure Refuse is conveyed to a sharply inclined grate that has no moving parts like conventional stokers. Gravity does much of the work in moving the material. Underfire air flows upwards through the grate, but a unique feature is a series of air discharge ports along the length of the grate, from which sequenced pulses of air augment gravity to keep fuel flowing as it travels from top to bottom.

The pulsing system adds an additional fuel flow control method previ- ously not available for solid fuel combustion. The hot combustion gases flow to a heat recovery steam generator for steam production that may be used to drive a turbine for power generation.

Backend equipment on the unit includes a lime-fed acid gas scrubber and fabric filters for particulate and heavy metals removal. It traces back to German scientists who developed coal gasification for production of synthetic fuels in the s.

Later in the century, Dow Chemical Company took the process further by using coal gasification to produce power at the Plaquemine facility in Louisiana. The chemistry behind coal gasification is rather complex, but when viewed in simplistic terms, is readily understandable.

First, consider combustion of coal or any other fossil fuel in a conventional boiler. When the fuel is burned with suffi- cient oxygen, it oxidizes completely as follows:. Likewise, hydrogen in the coal combusts to water and sulfur burns to sulfur dioxide, which of course is a pollutant when released to the atmosphere. Department of Energy. The system was set up to repower an existing steam turbine and to add new generating capacity. Figure 2- 13 outlines the initial design.

The most important steps include the following:. Partial combustion of the coal takes place in this wne. The combustion temperature of 2,oF 1,oC exceeds the ash melting point, so slag flows to the bottom of the unit for extraction.

As it mixes with the hot gas rising from below, the fresh coal devolatilizes and breaks down, producing the final synthetic gas mixture. The gas then passes through filters that remove particulates, including unburned carbon. The H 2S-rich amine solution is routed through a steam stripper that removes the H 2S. The regenerated amine returns to the process, while the H2S is sent to a conventional Claus unit for conversion to elemental sulfur.

Some basic data, as reported by the DOE, are illustrated in Tables and 2- 2. Also of great importance are the emissions reductions, particularly for so2 and NOX. Both are well below current and projected future requirements. The Wabash River unit started up in and received final approval in The DOE reported on a number of problems that had to be solved during the commissioning period. First, the gasification process generated vaporous chlo- rides that poisoned the COS-H 2S conversion catalyst.

Retrofit of an additional scrubbing system removed the chlorides ahead of the catalyst bed. Candle ftlters for particulate removal were originally ceramic, but these fractured due to stresses in the system. Metallic filters solved this problem. Ash deposits in the fire-tubed flue gas cooler created difficulties that were solved by modifications to the flow path and geometry, and by periodic mechanical cleaning of the tubes.

The H2S removal system was initially undersized; capacity was increased. However, an advantage of the com- bined-cycle concept is the gas turbine may be fired with natural gas during peri- ods when the gasifier and its auxiliaries are down for maintenance. Perhaps the most important point about integrated coal gasification com- bined-cycle systems is that coal rather than natural gas is the primary fuel in a combined-cycle process.

Energy personnel, politicians, and the media frequently comment on the need for a balanced energy policy. The ICGCC technique appears to offer good potential for the continued use of coal as a power generation fuel. Repeated below are the two most important reactions regarding the S02 removal process in a circulating fluidized-bed boiler.

At the same time, bed temperatures in the two units rose approximately 60"F to 70"F 16''C to 21"C , and NOx emission levels increased significantly, as well. Test per- sonnel concluded that the bed temperatures rose due to the greater reactivity of the limestone.

Once the change was made, limestone feed dropped almost by half, and the corresponding heat absorption also declined, resulting in increased bed temperatures. Utility personnel had to adjust fuel flow and other parameters to return the beds to normal temperatures.

Flow-assisted corrosion FAC is a phenomenon affecting many steam gen- erating units, causing fatalities at several plants. The flowing liquid gradually dissolves the protective magnetite layer at the point of attack, lead- ing to wall thinning and eventual pressure-induced failure Fig.

Typical HRSG configurations require many short-radius boiler tube elbows. The low-pressure evaporator, where temperatures may be at or near oF, can be particularly susceptible to FAC. Current and future plant designers, engineers, managers, and owners need to be aware of this problem and act accordingly. Fossil fuel composition and combustion products also influence selection of boiler materials. This chapter examines fuel and ash properties in more detail.

CoAL Coal is compressed plant matter that over millions of years transformed into a high-carbon material. Age, type of initial vegetation, and location of deposit for- mation are all significant factors in the quality of a coal deposit. Scientific research indicates that the first plants to grow on land appeared more than million years ago during the Silurian and Devonian periods of the Paleozoic Era.

This early vegetation consisted mosdy of leafless shoots. Some million years ago, extensive forests covered much of the world, and it is approximately from this time that coal deposits have been dated. The period from to million years ago is known as the Carboniferous period, and during this time many coal deposits originated.

This was a period of globally warm temperatures, which encouraged plant growth. Indeed, plants and vegetation grew to unimaginable sizes when compared to our current world. Giant ferns and plants the size of current-day mature trees were quite common. At the end of the Carboniferous period-and for about million years thereafter-coal formation in the Northern Hemisphere greatly diminished.

With the onset of the Cretaceous period in the Mesozoic Era around million B. Thus, the coal that we use today developed over hundreds of mil- lions of years from a wide variety of vegetation. What was the process behind coal formation? To understand the general properties of coal, it is first necessary to understand the basic chemical composition of plant life. What is important to know is that the main building block of vegetation is cellulose.

Cellulose belongs to a class of com- pounds known as carbohydrates, whose name comes from the fact that the com- pounds are composed of carbon, oxygen, and hydrogen. Cellulose fibers within a plant are held in place and bonded by another carbon-based polymer known as lignin. Together, cellulose and lignin comprise the bulk of plant material, although other natural compounds such as hemicellulose and resin are present.

In each com- pound, the primary elements are carbon, oxygen, and hydrogen. The prerequisite for coal formation were the vast swamps that covered much of the earth in prehistoric times. Vegetation that dies upon firm ground is decom- posed by the atmosphere into carbon dioxide and water.

When vegetation dies in a swamp, a much different process occurs. The first step is bacterial attack of the dead vegetation. Microorganisms consume hydrogen and oxygen, increasing the carbon content. This mechanism, known as the biochemical phase of coalification, is self-limiting, as the bacterial action produces organic compounds eventually becoming lethal to the organisms themselves. Over time, the partially decomposed matter becomes overlaid by other material, including more vegetation and soil.

This process has two principal effects-it places the material under increasing pressure and moves the deposits deeper underground where temperatures are warmer. Table : Change in chemical composition as a result of coalification Reproduced with permis- sion from Steam, 40th ed. The combination of pressure and heat causes additional loss of oxygen and hydrogen.

This is known as the geochemical phase of coalification. The results are graphically illustrated in Table , which shows the primary chemical composi- tion of the plant material from wood to the most mature of coals-anthracite.

The principal point is that as a coal matures, carbon content increases. Theoretically, a completely mature coal would have the chemical composition of graphite.

Complex carbohydrates within vegetation are created from sugars and starch- es that the plant produces through photosynthesis.

During the coalification process, these compounds and others metamorphose to low-weight organic mol- ecules that are not bound to the main coal structure. The smaller organic com- pounds are known as volatiles because they vaporize with increasing temperature. Volatiles are driven off during the coalification process, and increasingly mature coals contain less volatile content. One might be tempted to think that age is a primary factor in the maturity of coal.

While this is true in some cases, the two most important factors are pressure and temperature. Coals that were buried deep and located in high temperature zones-underneath a region of volcanic activity-mature much more quickly than older coals subjected to less heat and pressure. Agglomerating Character. Low volatile Uituwmou'l coal I L Hitmnhwu:'! High volatilf' C bituminous 'oal : ll,GOO 13, l Subbiturninous 2.

A 6,:! Lignitie 2. Schuylkill 4. Lackawanna 2. Montgomery 2. McDowell 1. Cambria 1. Somerset 1. Indiana 1. Westmoreland 1. Pike 2. Williamson 5. Emery Vermilion 5.

Sheridan Campbell Mercer Calculations by Parr formulas. Table Properties of some U. Tables and list the ASTM classification and characteristics of coals. Let us use them to examine fundamental chemical properties and heating values of coal. We will then take a close look at the impurities that reside within coal deposits, and how they behave during the combustion process. Examples of the different types of coal can be found throughout the world.

In the U. The state of Illinois also sits atop an extensive bituminous deposit. A large subbituminous deposit resides beneath the states ofWyoming and Montana, and because much of this coal is mined in an area near the Powder River, is known as Powder River Basin PRB coal.

Significant lignite deposits are located in North Dakota and to a lesser extent in Texas. Around the world, China has large bitu- minous and lignite deposits; Russia has enormous deposits of bituminous coal and some lignite in many different areas; Germany has significant deposits of bitumi- nous and brown coal an immature lignite ; and Great Britain is endowed with large reserves of bituminous and anthracite. In the southern hemisphere, Australia has significant deposits of bituminous and brown coal.

Fossil Fuel and Ash Properties I Peat A visual examination of peat provides a clear example of the intermediate stage between plant life and coal deposits.

Peat may range from a light-colored substance that has recognizable pieces of plant matter to a black material that looks like coal. Although peat is continually being compacted by overlying material, it is still subject to microbiological decomposition in the biochemical phase of coalifi- cation.

One of the byproducts of this process is methane, which is commonly referred to as "swamp gas" or "marsh gas. The typical aging process for peat involves a general rule that it takes years for a 2- to 3-inch layer of peat to form. Some modern swamps have peat lay- ers up to 30 feet deep, which means they have been undisturbed for thousands of years. Not uncommon are layered coal deposits, where each seam is separated by soil and minerals. This suggests that some ancient swamps produced a layer of peat, died out, then redeveloped to start the process over again.

Lignite Continued compression and heating of peat produce lignite and its more immature precursor-brown coal. While peat is not considered to be coal, lignite definitely falls into the coal category, although plant material is often still clearly evident in lignite deposits.

This is the first fuel listed in the ASTM coal classi- fication table, and as is clearly evident, the heating value quantity of energy avail- able from combustion is the lowest of all coals, with a range of 6, to 8, Btu per pound 14,, kJ per kilogram on a moisture and ash free basis. Lignite-fired boilers are typically much larger in size than other boilers because long residence times are required to extract the energy from the fuel.

Lignite is not a common fuel of choice. It is mosdy used at mine-mouth power plants, in which the fuel is conveyed direcdy from the mine to the plant. Lignites contain much volatile matter and are the easiest coals to ignite. For the same rea- son, they are also the coal most prone to spontaneous combustion in coal piles and bunkers Appendix This must be taken into account when designing fuel handling and drying systems for lignite. Boiler two-drum arrangement, 8 Boiler water treatment, 31 Boiling point, 4 Brayton cycle, 42 Bubbling-fluidized beds, G Gas analysis, Gas re-burning, Gas turbines, 42, 46, Grain elongation, Grain formation metals , 96, 95 Grain size metals , 95, Grandfathered plants, Graphitization, , Grate stoker , Gypsum, L Latent heat of fusion, 4 Latent heat of vaporization, 4 Light-off fuel oil, 68 Lignite, 60, 63 Lime scrubbing, Limestone scrubbing, 35, 37, 55, , Loss on ignition, 88 Lower heating value, 67 Lowest achievable emission rate, , , Low-NOx burners, , Methane, 70 Mineral relationships ash fusion temperatures , Mineralogy coal , 65, 74 Moisture coal , Molecular structure metal , Molybdenum content steel , 97 Mud drum cooling coil, 14 Multipollutant control strategies, T Technology, , Tensile strength, 99 Thermal insulation, 11 Time-temperature-transformation, Titanium, 99, Total alkalis slagging , Traveling grate stoker, 48 Trisodium phosphate, 31 Tungsten, 99, Turbulence, 6 Two-drum boiler, 8.

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