Boiler operations, restrictions

As a result of the need to prevent SCC, the standard water treatment program (as practiced by almost all HP boiler operators for many years around the world) has been to severely restrict or totally eliminate the presence of free hydroxyl ion in the boiler water. 

Restrictions Placed on the Boiler and Its Operation Many of the flue gas treatment system elements already discussed place restrictions on the boiler and its operation. Some examples of flue gas treatment system requirements that could restrict boiler operations would be the necessity for flue gas reheat, the ability of the flue gas treatment system to follow boiler load, the increased dust loading of dry systems, and the increased size and complexity of the system. In addition, many systems require a specific flue gas temperature for proper operation. This temperature requirement determines the location where the flue gas is subjected to treatment, thus affecting the design of downstream... 

When considering the need for capital pretreatment equipment, sufficient care should be taken not to propose any particularly sophisticated external or internal water treatment regimen that of itself creates restrictive operational BW control limitations—where boiler design, steam usage, and common sense dictate no necessity for such limitations to be imposed. The overall water treatment program should not be overdesigned but should properly match the needs of the project. 

Steam flow restrictions. Operating a boiler that has a restricted steam flow due to blockages or deposits in the chevrons, baffles, collecting pipes, splash plates, or pans (perhaps resulting from longterm adverse water chemistry conditions) may cause localized high steam velocities that lead to carryover. 

During the field demonstration in 1997 at the Department of Defense s (DOD s) Operable Unit 2, Hill Air Force Base in Utah, approximately 908 gal of dense, non-aqueous-phase liquids (DNAPLs) were removed from contaminated soils. The cost of the demonstration was 230/yd of soil treated and 165/gal of DNAPL removed. These costs included the purchase of all the equipment and an extensive monitoring network. It is estimated that future applications at the site would require roughly half as many wells and the boiler rental would be restricted to a much shorter period. These conditions would lower the direct treatment costs to 103/yd of treated soil and 74/gal DNAPL removed (D18518W, p. 216). 

The initial visual SEM examination of the bed sample clearly indicated agglomerated material. In this case the automated EDS-analysis could be restricted to determine the ten elements in the adhesive material of the agglomerate and the bed particles could easily be excluded from the analysis. Since it is known that high chlorine content in straw causes fouling and corrosion during normal operation of the boiler, a few point analyses were carried out in the initial examination to explore the chlorine content in the agglomerate. It turned out that there is no or very little chlorine in the adhesive material. 

With minimum air supply, the percentage of CO2 in the flue gases (the amount of which is constant) is a maximum. Hence, the significance of CO2 determination as an index of boiler efficiency 16 per cent by volume represents remarkably good operation. The sum of CO2, CO and 0 in the gases will almost invariably exceed 19 per cent. Air supply so restricted or so badly distributed as to lead to the presence of even small percentages of CO is highly wasteful even 0.5 per cent may imply a 5 per cent loss of fuel. 

Restrictions on the maximum furnace heat liberation allowed vary. The size and number of safety valves may also vary. In addition, personal wishes of the users and their financial and operating policies can influence the design and price of a boiler installation considerably. 

This means that the electrical work that is produced is only slightly less than the decrease in enthalpy in the reaction. Note that if we simply let the reaction occur without producing work, the quantity of heat, — AH, would be released. This could be used to heat a boiler which in turn could run a turbine. But this heat engine is subject to the Carnot restriction the electrical work that could be produced by a generator operated by a turbine would be... 

Operating data indicate that Sirotherm TR-20 reins can produce waters of salinities as low as 50-100 ppm dissolved dalts, the economic upper range of salinities in feed water being restricted to 2000-3000 ppm. The resins are expected to find application in the demineralization of mildly brackish surface and underground waters for industrial and municipal use and as a roughing stage in the production of high-quality boiler feed water. 

A boiler rupture occurs if steam flow output is prevented or restricted and the temperature and pressure in the boiler increases. If some form of safely device is not provided or is inadequate to limit the pressure to a safe value, the boiler will rupture. Boilers are required to be equipped with safety valves to relieve pressure if they exceed set values. Low points in some boilers are provided with fusible plugs. During normal operations, the plugs are covered with water which keeps them cool. If the water level drops and they are exposed, the plugs melt and create another vent for pressure relief. Boilers also have low-water shutoff devices which block in the burner fuel when the steam drum water drops below a certain level. 

Boiler Top Dome Weld Inspection Figure 7 shows an example of how the KITSCAN has been adapted to suit a specific inspection requirement. The brief was to examine ultrasonically a large 2.6m diameter weld which formed part of a nuclear boiler structure. The inspection had to be conducted from within the boiler, to which access was gained though a 27" diameter manway. The condition inside the reactor required operators to wear contamination proof clothing and air hoods. Previous inspections had been carried out using manually operated scanners with the analysis equipment located outside of the boiler due to the restricted access conditions the entire... 

Confined spaces—For welding or cutting operations conducted in confined spaces (i.e., in spaces that are relatively small or restricted spaces, such as tanks, boilers, pressure vessels, or small compartments of a ship), personal protective and other safety equipment must be provided. Protection of personnel performing hot work in confined spaces includes adhering to the following ... 

The more usual description for section 606 is confined conductive locations. These are spaces where freedom of movement is restricted and the body is likely to be in contact with exposed and extraneous conductive parts. This section covers work inside boilers, metal ventilation ducts and tanks, for example, where extensive contact with the metalwork increases the indirect shock hazard. The risk is enhanced if these interiors are wet or so hot that the operator s clothes are soaked with perspiration. Incidentally, although not... 

Treatment for carryover. Carryover of boiler water with steam is first minimized by proper boiler design. Close attention to operating practices, including restricting load swings, carrying proper water level, etc. should be the second approach to reduce susceptibility to carryover problems. The last approach to be considered, is be the use of anti-foams. When the application of anti-foams is the only solution to problem attention is drown to the synthetic products. There are two major classes of anti-foam used in boiler waters - polyamide and polyoxy anti-foams. 

Catalysts may therefore be designed for nse in specific duties. For power plant, the design must balance the reaction rates of NOX reduction and sulfur dioxide oxidation in the restricted range of temperature of flue gas leaving the boiler, or at the dust and sulfur dioxide removal stages. A low activity catalyst that reaches maximum NOX reduction between, say 380°-400°C, can be more efficient than a catalyst that is more active between 300°-350°C because, overall, it produces less sulfur trioxide at the fixed operating temperature. ... 

---