Boiler steam side

Boiler Steam Side Overpressure - All fired boilers are normally provided with PR valves sized to relieve the full steam rate in the event of closure of the normal outlet. 

I well remember one Louisiana refinery in which boilers and heat exchangers suffered from constant steam-side corrosion and fouling. 

In a study by Andijani and Malik (2004), fire tube failure was reported in the oil-fired boiler, which was in service for 15 years. The fire tubes were located in the central portion of the boiler floor area situated about 1.5 m from the water drum. Fireside temperature was 1640°C (max), and steam side temperature around 455°C (max). 

Corrosion of boiler and superheater tubes is sometimes a problem on the hot combustion gas side, especially if vanadium-containing oils are used as fuel. This matter is discussed in Sections 11.8 and 11.9. On the steam side, since modern boiler practice ensures removal of dissolved oxygen from the feedwater, a reaction occurs between H2O and Fe, resulting in a protective film of magnetite (Fe304) as follows ... 

With a few exceptions, coatings and linings are not used on the water and steam sides. In an EPRI project, about 50 turbine blade coatings have been evaluated, but none of these are being routinely applied. To reduce steam side oxidation in reheaters and superheaters, chromizing and chromating have been developed but these treatments are also not routinely applied. There is little use of composite materials with the exception of condenser tube sheets, which could be made of explosively clad stainless steel or titanium on carbon steel, and of the surfaces in the primary cycles of nuclear units where carbon or low alloy steels are protected by weld-deposited stainless steels. In pulp mill black liquor recovery boilers, stainless steel clad boiler tubes are often used. 

On Friday 9th March 1982, I had been working on shift as an Assistant Shift Manager on the steam side - i.e. the turbo-generator and boiler side of the plant -for maybe six months. I had still only been working at PFR for about 2.5 years, which I am sure most power station engineers would say is not enough time to be in a shift operations management role. 

Because the cumene production rate is to remain constant, the heat load on the reactor remains constant. Because overall flows do not change, the heat transfer coefficient remains constant. Because the reactor is not modified, the heat transfer area remains constant. Therefore, AT must remain constant. Because the original AT was 96°C, the following table gives the tenperatures that are required on the steam side. In order to produce higher-tenperature steam, the boiler feed water pressure, and therefore steam pressure, must be increased on the shell side. This is because the tenperature at which boiler feed water vaporizes to saturated steam increases with pressure. 

For the heat exchanger producing steam, there are two additional equations. One is the energy balance on the boiler feed water to steam side. 

Secondary systems. Boiler water. Chemical treatment of the water in the steam side of a fluid fuel reactor heat exchanger is a major... 

I well remember one Louisiana refinery in which boilers and heat exchangers suffered from constant steam-side corrosion and fouling. Investigation showed that the intake water-treatment plant operators would occasionally partially open the raw-water bypass around the entire treatment plant. They had a good reason, however, which they explained to me. "Norm, y all have to admit, some kind of water is better than no water at all."... 

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

Utility Baiances. The operating company should also require a balance for each plant utility. The most involved of the utility balances is usually the supply/demand steam tabulation showing all levels of steam and condensate and their interactions. The steam balance is almost always required at this stage for any required side studies. The steam balance influences many design parameters, such as boiler size and contingency, treated water makeup rates, blow -down disposal rates, chemicals usage, and surface condenser size. 

Gas versus steam turbines can involve a major side study. The result can be different for the process and utility sides of the plant as shown in Reference 13. For the gas turbine case, simple cycle versus waste heat boilers can be studied. Usually, waste heat boilers will win out unless the plant is in a cheap gas country. If gas turbines are selected for power generation, black start capability is usually a good investment. 

Early BWRs used an isolation condenser, although such is not specific to the direct cycle. This device removes decay heat by steam flow through a heat exchanger the other side of which is water vented to the atmosphere. Discuss the relative merits of such a boiler. 

Hot water boilers are potentially more susceptible to gas-side corrosion than steam boilers due to the lower temperatures and pressures encountered on low- and medium-temperature hot water boilers. With low-temperature hot water especially, the water-return temperature may drop below the water dewpoint of 50°C, causing vapor in the products of combustion to condense. This, in turn, leads to corrosion if it persists for long periods. The remedy is to ensure that adequate mixing of the return water maintains the water in the shell above 65°C at all times. Also, if medium or heavy fuel oil is to be used for low- or medium-temperature applications it is desirable to keep the heat transfer surfaces above 130°C, this being the approximate acid dewpoint temperature of the combustion gases. It may be seen, therefore, how important it is to match the unit or range of unit sizes to the expected load. 

Underfeed 0.3-2 600-900 Rank singles and doubles 1.0 Depends on retort depth On/off Manual or side screw automatic Small hot water and steam boilers... 

The early vertical boilers of dry-top design (steam on one side and hot combustion gases on the other side) were subject to the risk of overheating in any fire tubes located above the waterline, but these boilers could provide relatively dry steam with some degree of superheat. 

On a FT boiler, the main blowdown valve is always located at the bottom of the shell towards the rear of the boiler. On a WT boiler, blowdown valves may be located in the side of the top (steam) drum, the bottom (mud) drum, and the lower water-wall headers (sides, front, and rear). 

Most boiler plants with electrical power generating facilities employ surface condensers. These are shell-and-tube heat exchangers in either one-, two-, or four-pass configurations. Surface condensers typically receive cooling water on the tube-side and steam on the shell-side of the heat exchanger. The LP turbine steam generally is received at the top of the condenser and proceeds through the condenser in a downward flow, while the FW turbine exhaust steam enters at the side. 

Given 10,000 Ib/hr of 700°F cycle exhaust gas passing through a heat recovery boiler (HRB) (a) How much 150 psia, 400°F steam can be produced (b) How much heat is transferred from the gas to the steam (c) What is the exhaust temperature of the gas leaving the HRB and (d) Sketch the T-Q (temperature-heat) diagram for the HRB. Assume a gas side mean heat capacity of 0.25 Btu/lb, °F, an evaporator pinch temperature of 30°F, a feedwater temperature of 60°F, and an evaporator drum pressure of 180 psia to allow for pressure losses. 

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