Heat Exchanger Design Handbook, Second Edition,. Kuppan will be able to evaluate boiler and HRSG performance without assistance from boiler suppliers!. waste utilization HRSG draft designs for combustion plants in Russia and Germany were developed. - modern gaseous masout hot water boilers with capacity. a heat recovery steam generator (HRSG), a steam turbine generator and .. Brayton Cycle and “Bottoming System” of a boiler-steam turbine with Rankine Cycle.
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Basics of Boilers and HRSG Design. Uploaded by Download as PDF or read online from Scribd. Flag for Boilers--Design and construction. Basics of Boilers and HRSG Design by Brad Buecker The book serves as an introduction to fundamental HRSG boiler design for the operator. design aspects of package boilers and HRSGs. (The terms ''waste heat V Ganapathy. Heat-recovery steam generators: understand the basics. Chemical.
Florian Leordeanu. Table 2 shows the main features and the typical steam outputs that can be expected for each of the three types. In a steam system, are illustrated in Figure conventional steam generator, the This is because of efficiency of energy recovery. Steam temperature varies with gas inlet conditions, so performance should be verified at various off-design cases. There is only one evaporator, and the economizer. The exit gas temperature in a Several options for improving energy single-pressure HRSG decreases as recovery, even in a single-pressure the firing temperature increases.
For example, at different ambient conditions 2, 3. Assuming a rator, and economizer, are fixed once Also, a low approach point in the reasonable pressure drop in the super- U is computed. To calculate U one fired mode could result in steaming heater, we can determine the saturation should have such mechanical data as in the economizer under unfired temperature t s at the evaporator. Economizer steaming Once the pinch point is selected, we But if U is not known, US is, which should be avoided, as it results in know the temperature of the gas leav- indirectly fixes the surface areas.
The heat loss hl ranges from we have indirectly established. It may also 3. AT in the evap orator and thus the need approach are selected in the fired Considering the energy balance for large surface area. The pinch point in mode.
This is why extended desired under unfired conditions. If Q1. The conditions and can be controlled pinch and approach points and per- superheater duty is: From Figure 2, con- performance of single, multiple- determined, since all the other data are sidering the heat balance across the pressure unfired and fired HRSGs known.
Simulation gives a good idea The economizer energy balance glecting blowdown, we have: Simulation can also help one this. Then in the off-design case, the values of US are corrected for the effects of gas flow, temperature, and composition.
Then, the energy transferred across each surface is obtained through an iterative process using the following equation after first assuming a steam flow rate to begin: This is why we cannot arbitrarily This, too, is an invalid temperature all the surfaces. This information is select pinch and approach points and the profile.
With a much higher pinch then used to correct the assumed exit gas temperature. This illustrates why The problem gets more complicated if various steam conditions for a typical gas pinch and approach points are best there are several modules, and gets turbine and the results are presented in selected in the unfired mode, having complicated further still if auxiliary firing Table l. It may be seen that as the steam values in the range suggested in Fig- is used to generate the desired steam flow pressure increases, the exit gas temperature ure 2, to ensure valid temperature rate in a particular module.
Simulation increases. Also, as the steam temperature profiles. Simulation can also help de- software, which performs these complex increases at a given pressure, the amount of termine valid conditions.
Large cogeneration and Let us now see that an exit gas temperature conditions or steam parameters. From Eq. Using Eq. The superheated steam temperature in a HRSG is controlled using spray desuperheaters as in conventional boilers. Steam temperature varies with gas inlet conditions, so performance should be verified at various off-design cases.
Multiple-pressure steam generation is employed in cases where the exit gas temperature from single-pressure-level generation would be considered too high or uneconomical. There are three types of HRSGs: This is not a rigid classification, but it is widely used. Table 2 shows the main features and the typical steam outputs that can be expected for each of the three types.
Figure 4b also shows a freshair-firing system, where a supplemen tary-fired HRSG is operated using air from a fan, a situation that arises, for example, when the gas turbine trips or is shut down for maintenance. Fig ure 4c shows a typical duct burner for a supplementary-fired HRSG. A simulation of the tempera - ture profiles must be performed I before designing the steam system for a given application. Unfired and supplementary-fired HRSGs are similar in appearance and constru ction, both being convective designs.
The units are internally insu- lated with ceramic-fiber insulation with an alloy steel liner to hold the insulation in place. The insulation thickness ranges from in. Roughly two-thirds of the HRSGs purchased today are unfired due to their low first cost. This is because a large surface area is required in these systems as a result of the low pinch and approach points and the low logmean temperature differences at the various heating surfaces.
Extended surfaces make the HRSG design very compact. And, lower gas pres sure drops can be achieved with extended surfaces than with bare tubes Table 3 2. Fin height can vary from 0. Fin thickness is typically from 0.
A low fin density is recommended for superheaters due to their low tube-side heat-transfer coefficient 3. Using a high fin density when the tube-side peratures remain safely within limits. The use of fins, in gen eral, high-gas-temperature zone use bare with a lower fin density can transfer the increases the tube wall and fin tip tubes, and subsequent tube rows, same duty.
Therefore, one should look temperatures and the heat flux inside the where the gas is cooler, have extended at the product of overall heat -transfer tubes. When the tube-side co efficient is surfaces. Table 4 illustrates the effects of fin in high tube wall and fin tip The higher the fin density and the ratio geometry on superheater performance temperatures even without fins.
For example, a superheater can In fired units, a combination of bare and area, the lower the gas-side heat- transfer the same duty with signifi- finned tubes is used to en sure that the transfer coefficient and hence the lower cantly different surface areas - the tube wall and fin tip tem - the overall heat-transfer co efficient surface area in case 2 is more than Figure 6 2, 4.
The gas pressure drop across the duct burner is low on the order of 0. This is important because each additional 4 in. In large capacity units for combined- cycle plants, reheaters are installed in addition to superheaters to improve the Rankine cycle efficiency. Unlike in a Rankine cycle system based on a conventional steam generator, where the condensate is heated in external steam-to-water heat exchangers using steam extracted from the steam turbine, in a gas turbine HRSG the double the surface area in case l, yet condensate or make-up water is heated such as natural gas and distillate oil the duty or energy transferred is es- in the HRSG itself to improve the into the exhaust gas stream.
This is because of efficiency of energy recovery. Generally, no additional air is used, the poor fin configuration in case 2 - Deaeration steam may also be gener- except when the exhaust gas is due to the higher heat flux inside the ated in the HRSG for the same reason.
Multiple pressure- oxygen available for combustion. In case 2 are much higher than in case 1. Compar- ing cases 2 and 3 illustrates how more duty is transferred with a lower sur- face area simply by selecting opti- mum fin configuration.
Thus, engi- neers and purchasing managers should not make decisions using a spreadsheet that shows only the sur- face areas of different designs.
Rather, a good evaluation should in- clude the product of overall heat- transfer coefficient on an external surface area basis and surface area. A duct burner typically has a rectangular cross-section and fits into the ductwork carrying the exhaust gases. The sections.
In certain plants Auxiliary firing and [ , Thus, the overseas, even solid fuels such as coal system efficiency exhaust gas still contains more than have been fired in these boilers using Typical gas turbine exhaust contains This is A HRSG simulation program has been The gas pressure drop across the adequate to fire additional fuel in the used to evaluate the efficiency of register burner is high about in.
The re- formance, and the results are present ed lationship between oxygen availability in Table 5 and Figures 7 and 8.
There are two reasons for this: We know from basic combustion principles that in a conventional steam generator, as the excess air increases, the efficiency decreases. In a HRSG, on the ments are similar between natural- other hand, the amount of excess air is and forced-circulation units.
Improving HRSG efficiency 2. The exit gas temperature in a Several options for improving energy single-pressure HRSG decreases as recovery, even in a single-pressure the firing temperature increases.
In a steam system, are illustrated in Figure conventional steam generator, the This reduces the amount of decreases as steam generation steam required for deaeration, im- increases. This results in a larger heat proving the overall efficiency. If sul- sink at the economizer and hence a furic acid vapor is present in the ex- lower exit gas temperature. Note that haust gases, the condensate tempera- in a HRSG, the gas flow remains ture should be no lower than the acid nearly the same at all steam vapor's dew point to prevent conden- generation levels.
Saturated steam is tube 4. Nozzle connections, steam purification equipment and internal piping, drum saddles. Staggered or Inline tube pitch All welded header design Fully drainable and ventable Fully top supported pressure parts Staggered or Inline tube pitch Similar to other system Economizers in design approach except: Multiple tube and finning material options based on considerations of oxygen pitting on the tube inside surfaces gas side fouling on the tube outside surfaces acid dewpoint considerations due to sulfur in the fuels.
Splitted bottom header for first pass utilized in area of water entry to avoid damage due to thermal shock Can be fabricated from Austinetic or Ferritic tube material depending on requirements. Single or two-stage purification system can be provided depending on facility requirements for steam.
Horizontal or vertical configurations Tray type or Spray and Tray type designs Connected directly to LP steam drum with no intervening valves. Floating Pressure operation.
Isolation dampers and silencers can be included as necessary in the stack assembly. Supplied in a variety of arrangements based on shipping limitations and field construction needs. Installed in stack above breeching to reduce heat loss.
Shipped in match marked pieces after shop pre-assembly. Stair access on one side, ladder access on opposite side. Open bar type grating with supporting steel. Provided for access to equipment in the following areas: Modular Box Design Approach: Highest degree of shop modularization with tube bundles shipped with the casings and supporting structures shop installed.
In some instances, steam drums and interconnecting piping can be shop installed. Requires a detailed and thorough review of shipping clearances to assure access to the site. Field Modular Design Approach Configuration based on maximizing the tube bundle size based on shipping limitations.
Heat transfer sections are prefabricated in modules tube bundles with interconnecting piping installed. Structural support steel and casing panels are shipped separtely from the modules which permits earlier site work and pre-assembly. This approach can support either top loading or side loading of the tube bundles and can support any sequence of installation left side first, right side first, front to rear, rear to front. Field Platen Design Approach Configuration based on very low component weights to facilitate inland transportation.
Interconnecting piping is shipped loose. Field assembly sequence is more restrictive due to installation hardware for the platens and would need to be determined prior to shipment of components. GE LM Fuel: Natural Gas. HP HRSG Overview. Flag for inappropriate content.
Related titles. Jump to Page. Search inside document. Multiple tube and finning material options based on considerations of oxygen pitting on the tube inside surfaces gas side fouling on the tube outside surfaces acid dewpoint considerations due to sulfur in the fuels Splitted bottom header for first pass utilized in area of water entry to avoid damage due to thermal shock Can be fabricated from Austinetic or Ferritic tube material depending on requirements.