Boiler types steel boilers

Thickness of shell should not be less than 12 mm. Boiler quality steel should be used since these units run at high internal temperature for long time continuously. Internal lining details (e.g. type of insulating and refractory bricks used, their alumina percentage, thickness of layer, castable refractory, expansion joints provided. (Vendor to submit copies of their test certificates giving chemical analysis, refractory properties, thermal conductivities if asked for by the purchaser. The expected maximum temperature at outer surface of the shell should not normally exceed 60—65 °C.)... 

In contrast to cathodic protection, anodic protection is relatively new. The feasibility of anodic protection was first demonstrated in 1954 and tested on a small-scale stainless steel boiler designed to handle sulfuric acid [23]. Anodic protection refers to the corrosion protection achieved by maintaining an active-passive metal or alloy in its passive state by applying an external anodic current. The basic principle for this type of protection is explained by the behavior shown in Fig. 5.40. 

This type of failure is generally encountered in pump shafts, heat exchanger tubes, rotors, steam turbine blades, aircraft wheels, boiler and steel equipment. Some major examples where corrosion fatigue is encoimtered are given below ... 

Carbon dioxide produces a solution of carbonic acid (as in boiler condensate, see Section 53.3.2). Carbon steel is often employed but corrosion rates of up to 1 mm/yr can be encountered. Coatings and non-metallic materials may be employed up to their temperature limits (Section 53.5.6). Basic austenitic stainless steels (type 534) are suitable up to their scaling temperatures. 

Electrical resistance boilers use banks of fixed, immersion-type, resistance heating elements (typically sheathed in seamless copper, Incoloy 800, or 316SS) to provide an energy source that is contained within a carbon-steel pressure vessel. The vessel is provided with a sight glass and all normal boiler controls, valves, and regulators necessary for automatic operation. The vessel is generally well insulated and housed within an enameled metal cabinet. Various electrical supply options are available. 

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. 

Because of their compact size, packaged vertical boilers can be custom-designed as a complete boiler plant system and simply shipped to the customer on a steel skid or platform. This type of system may comprise a dual boiler arrangement, with a pretreatment unit (water-softening and chemical-feed system), boiler blowdown and condensate return facilities, and also possibly a dual stack containing an economizer. This type of packaged system may reach 85% GCV efficiency. 

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. 

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. 

The corrosion of steel and other metals in a boiler system takes place when an electrochemical cell is established, although the rates of corrosion and the types of corrosion mechanisms involved are highly dependent on the particular circumstances that develop during the operation of individual boiler plants. A failure to adequately control corrosion ultimately leads to the failure of boiler surface components or other components and items of equipment in the system. 

This type of corrosion is liable to occur in any part of a boiler where silt, muds, scales, precipitants, or foulants exist and is by no means limited to ferrous metals. Stainless steels, brasses, and cupronickels are all subject to under-deposit corrosion and deep pitting. 

This type of stress-related corrosion process may result in boiler failure through a sudden and violent rupturing of the boiler tube metal. Austenitic stainless steels also are corroded by SCC mechanisms in the presence of concentrated chlorides (chloride-induced SCC). 

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

The use of hydroxyacetic/formic acid in the chemical cleaning of utility boilers is common. It is used in boilers containing austenitic steels because its low chloride content prevents possible chloride stress corrosion cracking of the austenitic-type alloys. It has also found extensive use in the cleaning operations for once-through supercritical boilers. Hydroxyacetic/formic acid has chelation properties and a high iron pick-up capability thus it is used on high iron content systems. It is not effective on hardness scales. 

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. 

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. 

A clamp-type pipe joint connector failed a short time after it was put into service. This clamp, shown in Figure 7.48, had been used to join two ends of NPS 8 carbon steel steam piping, operating at a pressure of approximately 11 MPa (1600 psi). The boiler feedwater used in this process had been softened by cation exchange (Ca <-> Na) and was fully deaerated. The feedwater was recycled water from an oilfield operation and contained several thousand ppm dissolved chlorides. The steam was 80% quality and at a temperature of approximately 330°C. 

The effluent from the reaction boiler is handled in type 310 (UNS S31000) SS above 800° F (425° C), type 321 or 347 (UNS S34700) SS above 500°F (260°C), and carbon steel below 500°F (260°C). Molten sulfur is handled in steam-traced steel or aluminum. At the discharge to the pits, oxygen causes severe attack on steel, so the discharge end of the steel line often contains a short piece of alloy 20. 

Steam sterilizers, or autoclaves as they are also known, are stainless steel vessels designed to withstand the steam pressures employed in sterilization. They can be (i) portable sterilizers, where they generally have internal electric heaters to produce steam and are used for small pilot or laboratory-scale sterilization and for the treatment of instruments and utensils or (ii) large-scale sterilizers for routine hospital or industrial use, operating on dry saturated steam from a separate boiler (Fig. 20.6). Because of their widespread use within pharmacy this latter type will be considered in greatest detail. 

In another type of dryer, steam is used to transfer heat into large steel rolls over which paper is passed at high speed to remove moisture added in the forming process (3). Typically, the paper web temperature is held to about 170°F. Steam is introduced to the rolls at about 50 psig, with about 2.2 pounds of steam needed to remove each pound of moisture. Process boilers are commonly fired by either residual oil or coal, augmented by waste material such as wood chips and spent pulp liquors. 

Fontes, Costa, and Azevedo [79] used 300 pm diameter Type R thermocouple in an alumina sheath with an external diameter of 4 mm and placed inside a 3 m or 5 m long water-cooled stainless steel probe to measure gas temperatures in a black liquor recovery boiler. Calculations showed the "true" temperature in the regions of highest temperature did not exceed measurements by more than 8%. Measurements were made at multiple elevations, multiple locations at each elevation, and at multiple insertion depths into the boiler. A traversing mechanism was used to insert the probe, which was checked frequently for deposition of black liquor particles and sulfate deposits. The temperatures ranged from approximately 700°C to 1000°C. 

Atmospheric particulate matter samples can be analyzed routinely for more than 50 trace elements. Trace element emissions arise from a large number of different source types in urban areas. For example, motor vehicles burning leaded fuel, electric arc steel furnaces, Kraft recovery boilers, and secondary lead smelters contribute to atmospheric lead concentrations. The wide spectrum of sources, together with the fact that trace metals often are only a minor fraction of the mass emissions from each source, obscure the relative importance of the contributors to atmospheric trace element levels. 

Kraft pulping chemical recovery consists of passage of black liquor along with the slurry passes through evaporators, recovery boilers, and causticizers to eventually produce white liquor. Corrosion on the fireside of the recovery boiler is accelerated by the presence of reduced sulfur species. The hydroxide mixtures present in black liquor are extremely corrosive to the recovery boilers made of type 304 stainless steel (37). Several phenomena in the recovery section cause different forms of corrosion such as (i) corrosion under ash build-up (ii) corrosion in the thin condensation layers and (iii) high-temperature metal/gas interactions. 

Sulfite pulping chemical recovery consists of greater amounts of sulfite, hydrogen sulfide, and hydrochloric acid than those used in the Kraft process. Because of these corrosive species, the internal portions of the recovery boilers and the evaporators are generally constructed of reinforced plastics, type 316L stainless steel, type 317L stainless steel, or nickel-based alloys. To prevent pitting and crevice corrosion, scale build-up should be prevented, wet-dry zones should be avoided, and chloride concentration should be kept to a minimum. 

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