Blow-down

As the water evaporates into steam and passes on to the superheater, soHd matter can concentrate in a boHer s steam dmm, particularly on the water s surface, and cause foaming and unwanted moisture carryover from the steam dmm. It is therefore necessary either continuously or intermittently to blow down the steam dmm. Blowdown refers to the controHed removal of surface water and entrained contaminants through an internal skimmer line in the steam dmm. FHtration and coagulation of raw makeup feedwater may also be used to remove coarse suspended soHds, particularly organic matter. 

Using combustion to stimulate bitumen production is attractive for deep reservoirs and in contrast to steam injection usually involves no loss of heat. The duration of the combustion may be short (days) depending on requirements. In addition, backflow of oil through the hot 2one must be prevented or excessive coking occurs (15,16). Another variation of the combustion process involves use of a heat-up phase, then a blow-down (production) phase, followed by a displacement phase using a fire-water flood (COFCAW process). 

Analysts should discuss sample-collection methods with those responsible. Frequently, the methods result in biased data due to venting, failure to blow down the sample lines, and contamination. These are limitations that must either be corrected or accepted and understood. Sampling must be conducted within the safety procedures established for the unit. Since samples may be hot, toxic, or reactive in the presence of oxygen, the sample gatherers must be aware of and implement the safety procedures of the unit. 

Dead legs in the sample line must be discharged safely to ensure that the sample will ac tuaUy be representative of the material in the unit. Without blowing down the dead leg, samples taken will be erroneous, as they may be representative of some past operating conditions. If the location is nonroutine, the sample leg may have accumulated debris. The debris could partially or totally block the line. Opening the isolation valve to blow down the line could result in a sudden, uncontrolled release, presenting a hazard to the sample gatherer. 

Blowing down Verify flow path before starting the flow. lines for cleaning., Blow (purge) lines to safe location which protects the operator and environment Wear proper personal protective equipment (PPE) Follow proper sampling procedures Use safe blow-down design CCPS G-22 CCPS G-23 CCPS G-29... 

The regenerator (Figure 4-80) is represented by a simplified model that ineludes the total volume and mass balanee ealeulation. The regenerator exit temperature is assumed eonstant for the duration of the transient. The third-stage separator is handled as a fixed volume and assoeiated pressure drop. Blow-down (bypass) flow is subtraeted from the input flow. 

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. 

Pipe with high resistivity lining that contains semiconductive or nonconductive flammable liquids should be blown down with nitrogen rather than air. To avoid pinhole damage, the flow rate during blow-down should be no higher than normal liquid flow rate. Also, the possible hazards created in downstream tanks by charged, two-phase flow should be considered (5-2.5.4). 

Use oxygen to blow down elothing, benehes or maehinery. 

Water flowed from the relief pipe (20 ft elevation) to tank E610. It first flowed through the jumper to the process pipe to the normally closed blow-down valve which was open (possibly inadvertently left open or failed to seat in the attempt to pressurize the tank). About 119 gallons of water flowed through this open blow-down valve, through another, normally open, isolation valve to enter tank E610, where it reacted with MIC. 

Often, the blowdown valve is routed to a closed flare system, which services other relief valves in the facility to ensure drat all the gas is vented or flared at a safe location. In such instances, a separate manual blow -down valve piped directly to atmosphere, with nothing else lied in, is also needed. After the compressor is shut down and safely blown down through the flare system, the normal blowdown valve must be closed to block any gas that may enter the flare system from other relief valves. The manual blowdown valve to atmosphere protects the operators from small leaks into the compressor during maintenance operations. 

Train all personnel in the functioning and value of blowdown during an emergency. This may be achieved by safety specialists explaining the various hazards and relative risks of blowing down and failing to depressurize. 

Umbildtmg,/. remodehng, etc. (see umbilden). umblasen, v.t. blow down. 

Used to summarize and detail the interrelationship of utilities such as air, water (various types), steam (various types), heat transfer mediums such as Dowtherm, process vents and purges, safety relief blow-down, etc., to the basic process. The amount of detail is often too great to combine on other sheets, so separate sheets are prepared. 

Public nuisance from boiler blow-down indicates collectors are needed. 

Disc/Seat Blow Down Ring Stem or Spindle Spring Bonnet Bellows... 

Makeup the water required to be added to the system to make-up for losses by evaporation, drift loss, and blow-down. 

Blow-down the amount of water continuously or intermittently removed from the system to maintain a predetermined water analysis with respect to chemicals and dissolved gases. The build-up of solid or chemical... 

L" Represents Net Woter Flow otter Evoporotlon, Mist ond Blow-down Losses. For Design Rotes Use L"nL. ... 

CR = cooling range, °F, difFerence between hot water into tower and cold water from the tower, °F B = rate of blow-down, gpm. (Because an acceptable level of concentration has usually been predetermined, the operator is more concerned with the amount of blowdown necessary to maintain the concentration. Equation 9-132.)... 

Example 9-15 Determinii Approximate Blow-down for Cooling Tower (Used by permission of Marley Cooling Tower Co., Inc., from Cooling Tower Fundamentals [144])... 

Even if the assumed evaporation and drift rates were perfecdy accurate, the calculated blow-down rate of 98 gpm might still not be quite enough because of the effects of air-borne contaminants, which are usually incalculable. Once the approximate level of blow-down has been determined, the circulating water quality should be regularly monitored and appropriate adjustments made. 

Figure 9-123. Cooling tower blow-down versus number of concentrations in circulating water percent of total circulating water to be wasted to maintain various concentrations. Used by permission of Hensley, J. C. (ed.) Cooling Tower Fundamentals, 2nd Ed. (1985), The Marley Cooling Tower Co., a United Dominion Co.

Despite the benefits of blow-down, however, chemical, electrostatic, or electronic treatment of the water is often required to prevent scale formation, corrosion, or biological growth. When treatment is required, or anticipated to be required, the services of a reliable water treatment company should be obtained. ... 

Brooke [234] provides calculation techniques using enthalpy of the air to determine water evaporated, air flow, and blow-down quantities. 

Performance, 387 Ground Area vs. Height, 391 Pressure Losses, 393 Fan Horsepower for Mechanical Draft Tower, 392 Water Rates and Distribution, 393 Blow-Down and Continuation Build-Up, 394 Example 915 Determining Approximate Blow-Down for Cooling Tower, 395 Pre-... 

Although these units find initial application in areas of limited water, they have not been limited to this situation. In many instances they are more economical than cooling tower systems and have been successfully applied in combination with cooling towers (see Figure 10-184). Economic comparisons should include such items as tower costs, basin, make-up facilities, water treatment, pumps for circulation, power supply, blow down, piping, etc. For small installations of air-cooled units, they should be compared... 

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