Combustion kraft mills

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

Subsequent to biosolids handling processes, kraft mills dispose of biosolids by land application, landfill, or combustion. 

EPA, 1996b. U.S. EPA, Office of Air Quality Planning and Standards, "Chemical Recovery Combustion Sources at Kraft and Soda Pulp Mills," EPA-453/R-96-012, Research Triangle Park, NC, October, 1996. 

National Emission Standards for Hazardous Air Pollutants for Primary Aluminum Reduction Plants National Emission Standards for Hazardous Air Pollutants for Chemical Recovery Combustion Source at Kraft, Soda, Sulfite, and Stand-Alone Semichemcial Pulp Mills National Emission Standards for Tanks—Level 1 National Emission Standards for Containers National Emission Standards for Surface Impoundments... 

Kraft pulp mills Digesters batch and continuous Multiple-effect evaporators Recovery furnace Weak and strong black-liquor oxidation Smelt tanks Lime kiln Mercaptans, methanol (odors) H2S, other odors H2S, mercaptans, organic sulfides, and disulfides h2s Particulates (mist or dust) Particulates (dust), H2S Condensers and use of lime kiln, boiler, or furnaces as afterburners Caustic scrubbing and thermal oxidation of noncondensables Proper combustion controls for fluctuating load and unrestricted primary and secondary air flow to furnace and dry-bottom electrostatic precipitator noncontact evaporator Packed tower and cyclone Demisters, venturi, packed tower, or impingement-type scrubbers Venturi scrubbers... 

Sulfates are discharged into water from mines and smelters, and from kraft pulp and paper mills, textile mills, and tanneries. Atmospheric sulfur dioxide, formed by the combustion of fossil fuels and by metallurgical roasting processes, may contribute to the sulfate content of surface waters. Sulfur trioxide, produced by the photolytic or catalytic oxidation of sulfur dioxide, combines with water vapor to form dilute sulfuric acid, which falls as acid rain . The environmental fate and transport of sulfate are inextricably linked to the physical and chemical processes active in the earth s sulfur cycle. 

Pollutants for Chemical Recovery Combustion Source at Kraft, Soda, Sulfite, and Stand-Alone Semichemcial Pulp Mills... 

In spite of these efforts to optimize the combustion of black Hquor together with many improvements of the energy efficiency of pulp and paper mills, there have also been activities to improve significantly the efficiency of the energy (i.e., the evident production of electric power) and chemical recovery cycle in kraft pulping by one... 

Black liquor from kraft or soda mills pulping hardwoods may present problems during its evaporation and combustion by conventional methods. These problems have been encountered with some eucalypt species, particularly with wood from trees of old age, and special measures may be needed to overcome the problems caused by extractives. Apart from the formation of deposits and scale, which reduces heat transfer in the evaporators, the extractives increase the viscosity (so that the evaporation process is affected) and reduce the swelling properties when incinerated, resulting in incomplete combustion (130). These difficulties with black liquor from the soda process can be avoided with the use of a wet oxidation process conducted under high pressure (97). 

According to Kraft and Kahles (45) the determination of carbon in refractory metals can be carried out as follows 0,5 to 1 g of low carbon iron is weighed into the prepared boat as lowest layer. Thereon, depending on the expected carbon concentration, 0.2 to 1 g sample (degree of fineness 0.2 mm or chips) is stratified and either 0.5 g tin millings or 0.25 g tin millings mixed with 0.25 g granulated bismuth are put. The combustion is carried out at 1350 to 1400°C, and carbon dioxide is determined by coulo-metry or conductometry. 

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