Boilers blowdown

The utility system also creates waste through products of combustion from boilers and furnaces and wastewater from water treatment, boiler blowdown, etc. Utility waste minimization is in general terms a question of ... 

Feedwater The feedwater for a steam cycle must be purified. The degree of purity depends on the pressure of the boiler. Higher pressure boilers require higher feedwater purity. There is some trade-off between feedwater purity and boiler blowdown rate. However, increasing blowdown rate to compensate for lower feedwater purity is expensive, because blowdown water has been heated to the saturation temperature. Typical feedwater specifications for utihty boilers are given in Table 4. To some extent turbine steam purity requirements determine the feedwater purity requirements. The boiler-water siUca required to maintain adequate steam purity for higher pressure steam turbines is considerably less than the boiler could tolerate if deposition in the boiler were the only issue. 

Phosphorus and compounds SPA Phosphoric acid Boiler blowdown Corrosion protection Detergents Fertilizers Matches Metal finishing... 

Ammonium Nitrate Plants - In ammonium nitrate plants, wet scrubbers can be considered for prill towers and the granulation plant. Particulate emissions of 0.5 kg/t of product for the prill tower and 0.25 kg/t of product for granulation should be the target. Similar loads for ammonia are appropriate. Other effluents that originate in a nitrogenous fertilizer complex include boiler blowdown, water treatment plant backwash, and cooling tower blowdown from the ammonia and nitric acid plants. 

With a blowdown vessel, these may be installed at ground level, and thus the water in them can be above the boiler blowdown valve. In this case, a drain valve for maintenance purposes must be installed at the lowest point in the line between the boiler and the vessel. 

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. 

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). 

Using a skimmer, the BD water is taken from close to the top surface of the BW, either from the side of the FT boiler shell or WT boiler top drum or from a top-mounted sparge pipe extending down 3 to 6 inches below the waterline (but above the top set of tubes in a FT boiler). Blowdown is provided on either a continuous blowdown or an intermittent blowdown basis. 

The usual response to the apparently high and out-of-specification result is to correct the problem by increasing boiler blowdown. The net result is an unnecessary waste of BD water and the heat associated with it. Consequentially, there is an unnecessary increase in fuel consumption. 

Commonly, phosphate or carbonate may be purposefully present in many boilers as a result of the application of certain internal precipitating treatment programs. Rather than providing a benefit, they can add further to the risk of deposition if the correct operational conditions are not maintained because adherent scales are produced rather than free-flowing sludges that are amenable to boiler blowdown (BD). 

The heat exchanger component of a boiler blowdown, flash steam, and heat recovery system (FSHR). 

Gestra (UK) and Highveld Instrumentation (South Africa). Boiler Blowdown and Flash Steam Recovery Systems. Technical and promotional literature. Gestra Aktiengesellschaft, Germany, 1990. 

Generally, water is used in this plant to cool, leach, filter wash, scrub, heat, and washdown. The unreacted ore is slurred and sent, along with chromium and other impurities originally present in the ore, to the treatment plant. The boiler blowdown, which is sometimes contaminated with chromium escaping from the process area, adds to the volume of wastewater coming from the plant. The non-contact cooling water from the plant contains dissolved sulfate, chloride, and chromate thus it is sent to a wastewater treatment plant. The scrubber water may be used to slurry the ore or discharged. 

As discussed under boiler feedwater treatment, boiler blowdown is required to prevent the build up of solids in the boiler that would otherwise cause fouling and corrosion in the boiler. Carry over of solids from the boiler to the steam system via tiny water droplets should also be avoided. Total dissolved solids (TDS) and silica (SiC>2), as measured by the conductivity of water, are both important to be controlled in the boiler3. Dissolved solids carried over from the boiler will be a problem to all components of the steam system. Silica is a particular problem because of its damaging effect on steam turbines, particularly the low-pressure section of steam turbines where some condensation can occur. Blowdown... 

Qloss = heat losses from the stack, casing and boiler blowdown... 

Improving the energy efficiency to reduce steam demand and hence reduce the wastewater generated by the steam system through boiler blowdown, boiler feedwater treatment and condensate loss (see Chapter 23). 

Increasing condensate return for steam systems to reduce makeup water requirements, reduce aqueous waste from boiler feedwater treatment and boiler blowdown (see Chapter 23). 

Wastewater, which is a basic source of emissions, can be categorized in five ways (1) wastes containing a principal raw material or product (2) by-products produced during reactions, (3) spills, leaks, wash downs, vessel cleanouts, or point overflows, (4) cooling tower and boiler blowdown, steam condensate, water treatment wastes, and general washing water and (5) surface runoff. 

Table 8 Range of Concentrations of Contaminants in Boiler Blowdown Waste...

The sulfuric acid plant has boiler blowdown and cooling tower blowdown waste streams, which are uncontaminated. However, accidental spills of acid can and do occur, and when they do, the spills contaminate the blowdown streams. Therefore, neutralization facilities should be supplied for the blowdown waste streams (Table 15), which involves the installation of a reliable pH or conductivity continuous-monitoring unit on the plant effluent stream. The second part of the system is a retaining area through which non-contaminated effluent normally flows. The detection and alarm system, when activated, causes a plant shutdown that allows location of the failure and initiation of necessary repairs. Such a system, therefore, provides the continuous protection of natural drainage waters, as well as the means to correct a process disruption. 

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