Soot blowing

Opacity reduction is the control of fine particulate matter less than 1 ixm). It can be accomplished through the application of the systems and devices discussed for control of particulate matter and by use of combustion control systems to reduce smoke and aerosol emission. In addition, operational practices such as continuous soot blowing and computerized fuel and air systems should be considered. 

High-pressure steam from steam soot blowers can easily cut through tubes, so correct alignment of soot blowing equipment is critical. 

Sudden reductions in steam pressure. Soot blowing or sudden, very high process steam demands can cause carryover. 

Load swings, water levels, soot blowing, BW total dissolved solids, BW alkalinity and other factors all affect steam purity. 

NOTE Soot blowing or operation of the bottom BD may adversely affect steam sampling studies. 

During soot blowing, a 10-fold increase in particulate emission concentrations was accompanied by a 30-fold increase in PCDD/F emission concentrations prior to the pollution abatement device. Accounting for particulate removal in the fabric Alter, an overall three-fold increase in PCDD/F emission concentrations was observed during periods of soot blowing. 

Excessive us of high-pressure steam soot blowers is a common source of tube erosion-corrosion. Other boiler cleaning methods less threating to boiler tubes are available such as mechanical rapping, shot cleaning, and compressed air soot blowing. 

The manual operation of water jets for on-line cleaning has been used for the removal of fouling deposits for many years, although modern soot blowing equipment is often preferred. Similarly shot cleaning, which involves the release of metal shot so that as it falls under the influence of gravity, it impacts the heat-transfer surface and removes any accumulated deposits. The technique is not widespread on account of the potential damage that could occur. 

Thermal conductivity of sintered and fused deposits found by the Australian researchers range from 0.5 x 10" kW/mK at 800 K to 2.0 X 10" kW/mK at 1500 K. This is consistent with the recent findings of Fetters et al. (3 ) for crushed deposits from a boiler fired with Indiana coal and with other literature values ( ). The increase of thermal conductivity of sintered and fused deposits is due to a decrease of void space and increased transmissivity of the material. Wall et al. emphasize that values of k obtained from ground deposits in laboratory studies are questionable since bounding of the deposit occurs in situ which leads to an increase of k. This agrees with our results for a 700 MW boiler which yielded an overall value of k - 3.2 x lO"" kW/mK for deposits which could not be removed by soot blowing (see below). 

Comparison of ZoloBOSS and optical pyrometer measurements in 274 MW coal-fired boiler. (Reprinted from Zolo Technologies, Inc., "ZoloBOSS Enables Intelligent Soot Blowing," Zolo Technologies, Inc., White Paper, 2009, http //www.zolotech.com/pdfs/case-study-... 

Vermiculite consists of a hydrated magnesium aluminium silicate that under the application of heat (in the temperature range 450 - 1200°C), can expand up to 15 times its original volume by the loss of the water of hydration as steam. Rapid incorporation of the aditive into a deposit weakens the deposit by the expansion of the vermiculite thereby facilitating deposit removal by soot blowing (see Chapters 15 and 16). 

Vitry (France) Screen tube deposits Reduced deposits. Reduction in soot blowing requirements... 

The technique most often employed in combustion systems to maintain efficient heat transfer across surfaces exposed to the flue gas, is the technique of soot blowing. The method was originally devised, as the name implies, to remove accumulations of soot from the internal surfaces of combustion plant, but it now has a more universal application for the removal of any deposits that may interfere with the heat transfer process. The use of additives (see Chapter 14) to modify the structure of slags and foulants, may improve the effectiveness of soot blowing equipment. 

Because of the damage principally erosion, that may arise from the use of soot blowers it is good practice to check the surfaces swept by the jets. If erosion does appear to be a problem it may be necessary to modify the cycle and duration of the soot blowing operation, or to reduce the steam or air pressure till acceptable conditions have been achieved. 

As the discussion demonstrates the design of soot blowing equipment is entirely empirical based on an evolutionary process. Nevertheless it is a technique that can be made effective in maintaining heat transfer efficiency in large scale steam raising plant. 

The sonic device or horn, generally operates at an audible frequency of around 220 Hz producing a sound not unlike that of a ship s foghorn with an intensity of around 130 dB. Low frequency resonant sound in the region of 0 - 20 Hz may be used to create a sound field for the removal of soot. An example of equipment for this duty consisted of a 5 m mild steel horn with a weight of 250 Kg. An activating air supply of 300 - 1200 rri h at about 5 bar was necessary for effective operation. The cost of such equipment is usually considered to be similar to the more traditional soot blowing facilities. 

In general the techniques described in Chapters 14 and 15 for the mitigation of gas side fouling are employed in combustion systems to reduce or eliminate the accumulation of deposits on heat transfer surfaces. Soot blowing and sonic... 

Accumulation of dust on the boiler tubes and walls is a significant problem and soot blowing is extensively required, usually using saturated steam. 

High exit-gas temperatures and high draft losses with normal excess air indicate dirty heatabsorbing surfaces and the need for soot blowing. 

In certain special circumstances - emergencies, startups, and shutdowns -model-predictive control cannot be used. It is more realistic to say that well-tuned, well-maintained model-predictive control application can emulate the plant s best operator - every minute of every day. Figure 4 compares the temperature response to a soot-blowing disturbance under three types of control. The solid line shows the open-loop (manual) response. The heavily dotted line shows better response with a PID (feedback) controller. The lightly dotted line shows superb response with model-predictive control. 

Adhesion characteristics of fly ash from U.S. coals to SCR catalyst, the effectiveness of soot blowing, and the effects of residual fly ash on catalyst activity. 

Breakdown of protective oxide layer and penetration of corrosive species in Alloy 625 SHT influenced by soot blowing. 

CRs and corrosion behaviors of the materials". It is known that the CR in the area affected by soot blowing in a WTE boiler is about 1.5-3 times greater than that in non-affected areas. This indicates the magnitude of the impact of temperature fluctuations on CRs. 

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