Boilers recovery

Through the use of lab tests implemented by the pulp and paper companies in the United States and Canada it was determined that all but one manual technique were both unrepeatable and inaccurate. During some years ago the operators of black liquor recovery boilers have been able to take advantage of the latest teehnology to inspect the wall thickness of the near drum generator tubes. The technology utilises immersion ultrasound and automated computer... 

Most recovery boilers use 63,5 mm OD carbon steel tubes in the generating bank. With a few exceptions these tubes are swaged at the ends to 50,8 mm. When the 63,5 mm raw tube is manufactured it is subject to a lot of specifications i.e. ASME. There are no specifications for the swaged end of the tube. This is unfortunate as the swaged part of the tube is subjected to further mechanical deformation dtuing the rolling procedure and is located in a wastage zone of tire recovery boiler. 

Wastage all around the tube is seldom seen near the tube sheet in recovery boilers. Figure 9 shows a sean of a tube that has gradual thinning around the full circumference of the tube with the wastage stopping at the tube sheet. 

Wood Pulping. The system Mg(OH)2 S02 H20 is also used in acid bisulfite pulping. Compared to a calcium-based system which is not as amenable to regeneration of the pulping bisulfite (87), fewer technical problems are encountered in the digesters, evaporators, or recovery boiler of the Mg-based process. In the presence of excess SO2, bisulfite forms in a 43% MgSO solution, at 25°C and 101.3 kPa (1 atm) SO2 pressure, to increase MgSO solubihty. 

Fig. 26. Schematic diagram of akraft recovery boiler, where ( " ) indicates primary and (-) secondary process streams (29).

Figure 3-19 shows the thermal efficiency of the gas turbine and the Brayton-Rankin cycle (gas turbine exhaust being used in the boiler) based on the LHV of the gas. This figure shows that below 50% of the rated load, the combination cycle is not effective. At full load, it is obvious the benefits one can reap from a combination cycle. Figure 3-20 shows the fuel consumption as a function of the load, and Figure 3-21 shows the amount of steam generated by the recovery boiler. 

Pulp and paper Kraft recovery boiler Soda recovery boiler Lime kiln... 

In the pulp and paper industry, the main gas emissions are from the pulp production. The main sources of emission are in the soda recovery boiler, lime kiln, evaporation plant, and bark combustion boiler. 

As discussed in Section 15.2.2, the gas turbine s main disadvantage is its low efficiency of around 25-35 per cent in open cycle. However, this can be significantly improved by the use of a heat-recovery boiler that converts a good proportion of the otherwise waste heat in the turbine exhaust gases to high-pressure superheated steam, which, in turn, drives a conventional steam turbogenerator for supplementary electrical power. This can increase the overall efficiency to 50 per cent for no further heat input as fuel. 

Dual pressure For comparison, a combined cycle scheme with dual pressure is shown in Figure 15.13. In this case, the waste heat recovery boiler also incorporates a low-pressure steam generator, with evaporator and superheater. The LP steam is fed to the turbine at an intermediate stage. As the LP steam boils at a lower temperature than the HP steam, there exists two pinch points between the exhaust gas and the saturated steam temperatures. The addition of the LP circuit gives much higher combined cycle efficiencies with typically 15 per cent more steam turbine output than the single pressure for the same gas turbine. 

Figure 2.6 (a) Small WT boiler, for HW/steam (b) large D-type, steam raising, industrial WT boiler (c) radiant WT boiler for utility power and (d) pulp mill recovery boiler, burning black liquor. 

If low-cost natural gas is available, a gas turbine can be used to generate power. In this case, the waste heat in the exhaust gas is used to produce steam in a heat recovery boiler (HR boiler). This approach also is used with some gas turbine plants (as in some high-speed navy vessels). Where an HR boiler is employed, if steam demand exceeds power demand, the boiler is fitted with auxiliary burners. 

Where propulsion is provided by diesel or gas turbine, it is common to use an auxiliary boiler in conjunction with a waste heat/heat recovery boiler (WH/HR boiler). The steam-HW mixture, produced by passing the exhaust engine gases over the HR boiler tubes, is piped to the auxiliary boiler steam drum and then mixes with auxiliary BW. All steam utilized by the ship is taken from the auxiliary boiler. 

The term waste heat boiler is also widely used to cover heat recovery boilers (HR boilers), which tend to be direct-fired steam generators, albeit employing low-grade by-product fuels such as bagasse, wood bark, com cobs, peanut shells, blast furnace gas, black liquor, and the like. 

Black Liquor Recovery Boilers Many special boiler designs have been developed around the world for the pulp and paper industry, including black liquor recovery boilers. 

Various permutations of the black liquor recovery boiler design are used to combust soda liquors in the soda pulping process and alkaline earth liquors and ammonium liquor (red liquor) in the sulfite pulping process. 

Enhanced Oil Recovery Boilers Enhanced oil recovery boilers provide HP wet steam for enhanced oil recovery. The steam is injected into oil-bearing strata, to heat the oil and reduce its viscosity, thereby increasing the potential for flow. 

Enhanced oil recovery boilers see also Boiler, enhanced oil recovery 58... 

Heat flux density Heat recovery boiler, see Boiler, water tube, heat recovery 219... 

Recovery boiler. The strong black liquor from the evaporators is burned in a recovery boiler. 

Power boilers at pulp and paper mills are sources of particulate emissions, S02, and NOx. Pollutants emitted from chemical recovery boilers include S02 and total reduced sulfur compounds (TRS). 

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