Boiler types shell boilers

This is the most widely used type of boiler in industry. The construction of a single-hue three-pass wetback shell is illustrated in Figure 23.2. As a single-hue design boiler evaporation rates of up to 16,300 kg/h F and A100°C are normal on oil and gas and 9000 kg/h F and A100°C on coal. 

For shell boilers, superheaters may be one of three types, depending upon the degree of superheat required. The first and simplest is the pendant superheater installed in the front smokebox (Figure 23.7). The maximum degree of superheat available from this would be around 45°C. The second pattern is again installed in the front smokebox but with this, the elements are horizontal U tubes which extend into the boiler smoketubes. The degree of superheat from this pattern is around 80°C. Third, a superheater may be installed in the reversal chamber of the boiler. A wetback chamber presents problems with lack of space, and therefore a semi-wetback, dryback or water-cooled wall chamber may be considered. Maximum degree of superheat would be around 100°C. 

Table 23.5 shows the recommended water characteristics for shell boilers and Table 23.6 the water quality guidelines for industrial watertube boilers. Due to the wide parameters encountered in the quality of feedwater, it is not possible to be specific and to define which treatment suits a particular type and size of boiler. The quality of make-up and percentage of condense returns in a system will both have to be taken into consideration. 

Advantages of this type include an ability to burn all fuels including those containing solid particles, good turndown ratio (4 to 10 1 typically) and an insensitivity to oil conditions such as pressure and temperature. It is widely used in shell boilers, and the only real limitation is that the cup surface has to be cleaned daily. The most common atomizer layout is shown in Figure 24.7. Variants include direct driven cup and separate mounting of the primary air fan. 

High pressure 2-50 MW Yes All types (mainly classes G and H) 6-20 20 3 1 to 12 1 Mainly wide-angle sprays in WT boilers, low excess operation Large shell boiler and watertube boiler process apphcations... 

Rotary cup 1-40 MW Yes All types (mainly class G) 2-3 60 3 1 to 15 1 Medium intensity, shape varied by register design Very popular for all sizes of shell boiler. Some use on process and WT boilers... 

Pulverized fuel burners 1-50 All types including anthracite hgnite and bituminous <15 1 None Limited use in shell boilers mainly kilns and power stations... 

Fluidized beds 1-50 All types of coal and waste sohd fuels 3.0 0.3-1.0m 2 1 and then by bed sectoring Removal and clean-up from bed Special vertical shell boilers and watertubes... 

The boiler water should be within the limits specified for that type of boiler by British Standards, DIN and similar standards. In a conventional shell type factory boiler the most important criteria are that hardness should be present only in very small concentrations, and the TDS should be below 3000 mg/1. 

There are four fundamental types of boiler available today—electric boilers, fire tube (shell or FT) boilers, water tube (WT) boilers, and nuclear reactor boilers. Electric boilers apart, all other types are essentially developments from shell and tube heat-exchanger designs. 

One of various types of valve employed to enable BD of a boiler. Main BD valves are located at the bottom of all boiler drums, shells, and headers. 

Waste-heat Boiler A shell and tube-type exchanger required to heat pressurized (4000 kPa) hot water from 117°C to a saturated vapour at 250°C. Design pressure on the tube side is approximately 5000 kPa. The waste-heat boiler cools reaction gases from 595°C to 280°C. It is made from mild steel. 

Figure 4.S. I (a) Some typical examples of different types of boiler defects. (Courtesy Milton and Leach ).(b) Examples of surface and buried defects in boiler and plates.T = endplate/tube plate thickness (mm) t = furnace or shell plate thickness (mm) o = depth of surface defect ...

If the CO is not completely combusted to CO2 in the regenerator, a CO boiler is used to complete the combustion. The resulting heat of combustion and the sensible heat of the flue gas along with any heat from auxiUary fired fuel are recovered in the form of high pressure steam. When the regenerator is operated in total CO bum, the CO boiler is replaced with either a shell and tube exchanger or a box-type waste heat boiler (see Heat... 

The overall efficiency of the condensing thermal cycle, as discussed, is dictated primarily by the steam conditions used. There are some small industrial stations with outputs up to 2 MW using shell-type boilers for the generation of steam. Here the steam conditions are limited to approximately 17 bara and 250°C. For larger installations these conditions will rise sharply when watertube boilers become attractive and more common steam conditions are of above 60 bara and 540°C. 

In the above example, a relatively complex steam generator of the watertube type has been adopted. Where lower-quality steam for process or fuel heating is required, a simpler shell (or firetube) design may be appropriate. In some cases, supplementary firing may be provided for the boiler, so further increasing plant complexity and with it the need for enhanced control and maintenance requirements. 

Chain grate 1-30 500-900 Rank normally washed smalls, but other types possible including high ash 1.7 80-150 mm 3 1 to 8 1 Manual drop tube boiler or drag link Shell and water boilers... 

Further boiler design developments produced various other types of compact, self-supporting, externally fired FT boilers, with the shell mounted over a steel-encased furnace. These designs were loosely called economic boilers and were typically coal- or oil-fired, three-pass boilers with an arched top (the crown sheet) and stayed side-sheets and other flat steel surfaces. 

Many boilers are fitted with a heat exchanger-type water sampling coil that permits the collection of a representative and cooled BW sample. The design generally provides for a coil of copper or stainless steel (SS) fitted inside a small SS shell. The unit is fitted with gate valves to control the flow of cooling water and BW. 

An internally positioned, removable steel cover for boiler shells and other types of PV. It enables inspections and cleaning to take place. 

Any of various types of heat transfer equipment, whereby relatively cold water flowing over a surface will, by conduction and convection means, transfer heat away from a process. The most common types of heat exchangers are plate and frame and shell and tube designs. A boiler is also a type of heat exchanger. 

The shell is constructed from carbon steel and will be fabricated from standard pipe of nominal size 30, schedule number 80. The 112 tubes required are 1.83 m (6ft) lengths and standard BWG 12. The tubes are made from stainless steel type 250 as recommended in the Australian Design Code AS1548 Design of Boilers and Pressure Vessels. 

In these types of heat exchangers the two fluids are separated by the tube walls. As one fluid flows through the shell— the region outside the tubes — the other fluid flows through the tubes. Heat transfer occurs so as to cool, and perhaps even condense, the hotter fluid, and heat, and even vaporize, the cooler fluid. Heat exchangers are called by various names depending on their function such as chillers, condensers, coolers, heaters, reboilers, steam generators, vaporizes, waste heat boilers, and so on. 

Shell-side effluent from the reforming exchanger is cooled in a waste-heat boiler, where HP steam is generated, and then flows to the CO shift converters containing two catalyst types one (4) is a high-temperature catalyst and the other (5) is a low-temperature catalyst. Shift reactor effluent is cooled, condensed water separated (6) and then routed to the gas purification section. C02 is removed from synthesis gas using a wet-C02 scrubbing system such as hot potassium carbonate or MDEA (methyl diethanolamine) (7). 

The synthesis loop consists of a recycle compressor, feed/effluent exchanger, methanol reactor, final cooler and crude methanol separator. Uhde s methanol reactor is an isothermal tubular reactor with a copper catalyst contained in vertical tubes and boiling water on the shell side. The heat of methanol reaction is removed by partial evaporation of the boiler feedwater, thus generating 1-1.4 metric tons of MP steam per metric ton of methanol. Advantages of this reactor type are low byproduct formation due to almost isothermal reaction conditions, high level heat of reaction recovery, and easy temperature control by... 

The exothermic reactions occur in a reactor containing tubes packed with a precious metal catalyst on a silica support. Heat is removed from the reactor by generating steam on the shell side of the tubes. Water flows to the reactor from a steam drum, to which makeup w-ater (boiler feeder water BFW) is supplied. The steam leaves the drum as saturated vapor. The reactions are irreversible and the reaction rates have an Arrhenius-type dependence on temperature. 

The Shell DeNO process as an add-on process is of interest for a wider range of applications. In addition to the treatment of gases from combustion sources such as furnaces and boilers, we may also consider NO removal from heaters, gas turbines, stationary reciprocating gas engines, etc. The modular construction of the PPR and LFR makes these types of reactor suitable for a wide range of reactor sizes, down to relatively small ones. We may also foresee applications in the treatment of NO -containing waste gases from the chemical industry, e.g., in nitric acid and caprolactam production or in catalyst manufacture. 

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