Boiler Feed Water Preparation

The recovered steam condensate may often be contaminated with oil. As the condensate will flow into the lower portion of the deaerator, this possible oil contamination must be removed to protect the boiler 

Low-level oil contamination (5 mg/1) can be removed bypassing the condensate through clay, or diatomaceous earth, either as a bed supported by anthracite, or diatomaceous earth precoat filters supported by filter paper, porous stone, or wire cloth etc. In addition, a small amount of earth is fed continuously with incoming condensate at the filter inlet. The filter cake is later removed by back washing and rinsing. 

Condensate with heavy oil contamination can first be treated by oil skimming or settling, or otherwise must be simply sent to the effluent treating facility. 

The main advantages of cation-anion ion exchanger resin demineralization over phosphate treating or hot-lime softening of boiler feed-water is the superior reduction of silicates in steam. Silicates deposited on steam turbine blades may lead to a loss of turbine efficiency and vibration, and also stress corrosion, and sudden failure of the blades. 

Such a demin plant consists of a cation exchanger resin bed followed by an anion exchanger resin bed. These resins look like small yellowish plastic beads and remind me of fish eggs (see Fig. 22.5). 

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Far less than the stoichiometric amount of sequestrants precipitation of insoluble salts from water hardness can be prevented by slowing down the formation of crystals and crystal growth. This process is called the threshold effect. It has long been used in the preparation of boiler feeding water, e.g., steam vessels of railroad engines. Originally sodium pyrophosphate was used for this task, but alkylphosphonic acids and derivatives thereof are superior in their effect. 

Reverse osmosis desalination plants consisting of 8 long tubular membranes prepared from commercial CA of D.S. 2.5 were set up for supply of drinking water and boiler feed water at two different locations. 

Utility functions such as the supply of steam and cooling water generally are set up to service several processes. Boiler feed water is prepared and steam is generated in a single boiler house. Noncontact steam used for surface heating is circulated through a closed loop, whereby various quantities are made available for the specific requirements of the different processes. The condensate is nearly always recycled to the boiler house, where a certain portion is discharged as blowdown. 

Historically, a classic example of an evaporation process is the production of table salt. Maple syrup has traditionally been produced by evaporation of sap. Concentration of black liquor from pulp and paper processing constitutes a large-volume present application. Evaporators are also employed in such disparate uses as desalination of seawater, nuclear fuel reprocessing, radioactive waste treatment,preparation of boiler feed waters, and production of sodium hydroxide. They are used to concentrate stillage waste in fermentation processes, waste brines, inorganic salts in fertilizer production, and rinse liquids used in metal finishing, as well as in the production of sugar, vitamin C, caustic soda, dyes, and juice concentrates, and for solvent recovery in pharmaceutical processes. 

Horizontal tube evaporators may be susceptible to vapor-binding, and foaming liquids cannot usually be handled. The short tube variety is seldom used today except for preparation of boiler feed water. The kettle-type reboiler is frequently used in chemical plant applications for clean fluids. 

We have a new, proprietary catalyst, and the kinetics are included in Table C.17. We would also like you to consider the economics of our continuing to use propylene with 5% propane inpurity at 0.095/lb versus purer propylene feed. In preparing this preliminary design, you should assume that all steam made can be used elsewhere in the plant with the appropriate economic credit, that condensed steam can be returned as boiler feed water for the appropriate credit, and that fuel gas can be burned for credit at its LHV (lower heating value). Additional information is given in Table C.18. 

Synthesis gas may be prepared by a continuous, noncatalytic conversion of any hydrocarbon by means of controlled partial combustion in a fire-brick lined reactor. In the basic form of this process, the hydrocarbon and oxidant (oxygen or air) are separately preheated and charged to the reactor. Before entering the reaction zone, the two feed stocks are intimately mixed in a combustion chamber. The heat produced by combustion of part, of the hydrocarbon pyrolyzes the remaining hydrocarbons into gas and a small amount of carbon in the reaction zone. The reactor effluent then passes through a waste-heat boiler, a water-wash carbon-removal unit, and a water cooler-scrubber. Carbon is recovered in equipment of simple design in a form which can be used as fuel or in ordinary carbon products. 

Far below stoichiometric amounts of sequestrants, precipitation of insoluble salts from water hardness can be avoided by the so-called threshold effect, in which formation of crystal nucleation sites is hindered by sequestrants. This process has been used for a long time to prepare feeding water for boilers e.g. steam vessels in rail way engines. Sodium pyrophosphate was originally used for this task. However, in particular alkyl phosphonic acids and their derivatives have a superior effect when compared to sodium pyrophosphate. 

A variety of reverse osmosis membrane systems based on cellulose acetate, aromatic polyamides, and other polymers have been tested for their potential applications. Reverse osmosis membrane equipment is available for large-scale operation since the process is widely used for the production of potable water from sea or brackish waters and upstream of ion exchange in the preparation of ultrapure water for steam-generating boilers. In these applications, the feed concentrations may vary from 500 to 40,000 mg/L of dissolved solids. The RO technique can be used at pH values between 3 and 12 and up to 45°C. 

Sodium hexametaphosphate (sometimes called Graham s salt) was first used in water treatment to introduce phosphate into boilers without producing precipitation in the feed lines. It was used in the preparation with 14 parts to 1 part of calcium and was essentially a softening process. Because of the mode of action and the extremely small amounts of the additive required, the technique was called "threshold treatment". An alternative name is sequestration. 

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