Surface Condenser Problems

Surface condenser problems. These include undersized surface condenser area, water-side fouling, lack of water flow, condensate backup, and excessive cooling-water inlet temperature. To determine whether a poor vacuum in a surface condenser is due to such heat-transfer problems, plot the same point on the chart shown in Fig. 18.4. If this point is on or slightly below the curve, it is poor heat transfer in the surface condenser itself that is hurting the vacuum. 

Condensate from contact units cannot be reused and may constitute a waste disposal problem. Surface condensers can be used to recover valuable condensate. Surface condensers must be equipped with more auxiliary equipment and generally require a greater degree of maintenance. 

As many emissions involve chlorinated compounds, corrosion is a major problem in many control methods. The corrosion of columns and surface condensers can be prevented or reduced by the correct material selection. However, corrosion remains a constant threat to the interior of incinerators. Additional pollution control equipment such as scrubbers may also be required to remove acidic compounds from treated gases before discharging into the atmosphere. 

The problem of corrosion debris and deposit pickup may happen anywhere in the steam distribution or CR systems (such as from a superheater, steam trap, surface condenser, FW preheater, or condensate tine). 

Oxygen and ammonia together create a serious problem. Copper and brasses used in surface condensers, LP FW heaters, fan-coil space heating units, and process heat-exchangers are particularly vulnerable, as... 

Particularly critical areas for corrosive attack include economizer tube inlet headers, certain boiler tube areas, surface condenser tubes, and HP heaters. Problems occurring here may be related to EC or perhaps to the dissolution of copper or iron and its transport to some point elsewhere in the boiler system. If transported metal reaches certain critical areas (such as copper reaching turbine blades), very serious outages may occur. 

Barometric condenser systems can be a major source of contamination in plant effluents and can cause a particularly difficult problem by producing a high-volume, dilute waste stream [8]. Water reduction can be achieved by replacing barometric condensers with surface condensers. Vacuum pumps can replace steam jet eductors. Reboilers can be used instead of live steam reactor and floor washwater, surface runoff, scrubber effluents, and vacuum seal water can be reused. 

Air-cooled surface condensers. Figure 8.11 shows a surface condenser elevated above the steam turbine. This creates an additional problem, in that moisture from the turbine exhaust steam will accumulate in the bottom of the turbine case. A special drain line from the turbine s case is needed to prevent condensate backup from damaging the spinning wheels. 

In Chap. 16 we reviewed several problems pertaining to steam jet precondenser and intercondenser problems. The surface condensers, which serve condensing steam turbines, are subject to all the same... 

The pressure in condenser A is greater than that in the surface condenser, and less than that in the final condenser (condenser B). This means that condenser A is operating at vacuum conditions. This prevents the condensed steam formed in condenser A from draining out to atmospheric pressure, unless the condenser is elevated by 10 to 15 ft. To avoid this problem, the condensate is drained back to the lower-pressure surface condenser. To prevent blowing the noncondensable vapors back to the surface condenser as well, a loop seal is required. The height of this loop seal must be greater than the difference in pressure (expressed in ft of water) between the surface condenser and the primary jet discharge condenser (condenser A). 

Condensate pumps serving surface condensers have a common problem. Their suction is under a vacuum. For example, let s assume the following for Fig. 18.3 ... 

But not for long. After 15 min of operation, the turbine speed slipped back down. Once again, I had lost a lot of vacuum in the surface condenser. Once again, the vapor outlet temperature had dramatically increased. But this time, the condensate outlet temperature had also increased. What was my new problem ... 

The gas that accumulates inside the surface condenser is called the noncondensable load to the steam jets. Some of the noncondensable load consists of C02 accidentally produced when the boiler feedwater is vaporized into steam. Air leaks through piping flanges and valves are other sources of noncondensable vapors. But the largest source of noncondensable vapors is often air drawn into the turbine case, through the shaft s mechanical seals. To minimize this source of leaks, 2 or 3 psig of steam pressure is ordinarily maintained around the seals. However, as the turbine s shaft seals deteriorate, air in-leakage problems can overwhelm the jet capacity. This will cause a loss of vacuum in the surface condenser. 

Most unfortunately, an incorrect correlation for heat-transfer coefficients for surface condensers has become widely disseminated in several books devoted to heat transfer. This correlation predicts heat-transfer coefficients, for clean condensers, of about 650, when the water-side velocity is about 6 ft/s. Use of this correlation has led to some extremely serious problems, with which your author is intimately acquainted. 

Another example of phase change during reaction is chemical vapor deposition (CVD), a process used to manufacture microelectronic materials. Here, gas-phase reactants are deposited (analogous to condensation) as thin films on solid surfaces (see Problem P3-25). One such reaction is the production of gallium arsenide, which is used in computer chips. 

The production of chilled water in the fine chemical manufacture and food processing industries may also give rise to freezing fouling where ice is formed on the cold surface. The problem may also exist in vapour systems during the recovery of solid products, e.g. the production of phthalic anhydride crystals in so-called "switch condensers". 

---