A. Ahlstrom Corporation

Kamyr, Inc.

Ahlstrom Machinery Oy

Andritz-ahlstrom Oy

Ahlstrom Machinery, Inc.

Erkki J Kiiskila

Joseph R Phillips

Rolf C Ryham

Brian F Greenwood

Johan E Gullichsen

Jan T Richardsen

Esko I Mattelmaki

Tuomo S Nykanen

Jarmo Soderman

Karl G Wiklund

Folke Engstrom

Kari Saviharju

Mikko Hupa

Bertel K Hakulin

Esa Vakkilainen

Nils E Virkola

Marjo Kuusio

Heikki Jaakkola

Jarmo Kaila

Henrik Eneberg

Pia Kilpinen

Markku Koskelo

Karl Wiklund

Olof Fagerlind

Pekka Tormikoski

Calcium carbonate scaling is inhibited in a multi-stage alkaline waste liquor evaporation plant in a chemical cellulose pulp mill having a bleaching plant. Calcium-containing effluent from the bleaching plant is treated together with alkaline waste liquor in the evaporation plant. A portion of the alkaline waste liquor of the evaporation plant is supplied to the bleaching effluent to increase the carbonate content of the effluent. Then the bleaching effluent is heated to 110-160&deg; C. by direct contact with a heating medium (e.g. steam, or secondary vapor) and maintained in a retention tank for a period of about 1-20 minutes to reduce the amount of dissolved calcium in the effluent. Finally the heat-treated bleaching effluent is evaporated with the alkaline waste liquor in the evaporation plant, with minimized scaling.

Inhibiting scaling in alkaline waste liquor evaporators

A method of removing nitrogen oxides from flue gases of a cellulose pulp mill recovery boiler does so in a cost effective and environmentally friendly manner. In the heat recovery section of the recovery boiler, a peroxide solution (e.g. a water solution containing about 1-35% hydrogen peroxide) is brought into contact with (e.g. sprayed into) the flue gases in the heat recovery section, so that the flue gases and the peroxide remain in contact between about 0.5-5 (preferably between about 1-2) seconds. The majority (e.g. about 60-90%) of the nitrogen oxides are converted to nitrogen dioxide. The temperature of the flue gases at the time of contact with the peroxide solution is between about 300-800.degree. (preferably 400-600.degree.) C. The nitrogen dioxide is removed by scrubbing the flue gases, downstream of the recovery boiler, with an alkaline liquid (e.g. a liquid otherwise used in the pulp mill having a pH of greater than 9) to convert the majority of the nitrogen dioxides into nitrate. The nitrate may be used as a nutrient in a biological effluent treatment plant within the pulp mill.

Method of removing nitrogen oxides from recovery boiler flue gases

A method of inhibiting calcium carbonate scaling in a multi-stage evaporation plant of black liquor by heat-treating calcium-containing liquor includes a first stage wherein the calcium-containing liquor is heated to about 110-145.degree. C. with direct contact with the heating medium; a second stage wherein the liquor is maintained at this temperature in a retention tank for 1-20 minutes to reduce the amount of calcium in the liquor by precipitating calcium carbonate; and a third stage wherein the heat-treated liquor is evaporated for combustion.

Method of inhibiting scaling in black liquor evaporators

A method is provided for reducing emissions of harmful nitrogen compounds from a pulp mill (e.g. kraft mill) having malodorous gases which include ammonia and reduced sulphur compounds therein. The method is practiced by (a) treating the pulp mill malodorous gases to lower the ammonia content thereof (e.g. by washing them with a bisulfite solution, such as one produced from washing flue gases with sodium sulphite), and then (b) burning the malodorous gases (e.g. in a dedicated incinerator, recovery boiler, power boiler, or lime kiln) under conditions which effect oxidation of reduced sulfur compounds therein (e.g. with an air excess of at least about 3% and a temperature of over 800 degrees C) so as to reduce odor emissions and emissions of harmful nitrogen compounds from the pulp mill. In the method (a) and (b) may be practiced using malodorous gas from a steam stripper as part of the malodorous gases treated, and the operating conditions, including the pH, of the stream stripper may be regulated in order to reduce the ammonia content of the clean condensate it produces.

Method of treating melodorous gases of a pulp mill

Effluents are minimized from a cellulose pulp mill having a recovery boiler by concentrating liquid effluents from the bleach plant and/or liquid spills from process streams, incinerating the concentrated effluents in the recovery boiler, removing particles present in the flue gases from the recovery boiler to produce an ash including salts containing potassium and chloride, and sulfur compounds, and removing the potassium and chloride from the ash while returning the sulfur containing compounds to the recovery loop, so as to balance the sulfur, chloride and potassium levels in the mill. The sulfur is typically returned directly to a stream of black liquor just before entry into the recovery boiler. Green liquor is produced from the melt, which preferably is treated to remove metals from it prior to caustization (e.g. by sedimentation and/or filtration), and prior to green liquor crystallization to produce sodium hydroxide.

Minimal effluents discharge pulp mill with chemical recovery

Apparatus for a pulp and paper mill, and methods of acting on liquid effluents produced in the mill, which minimizes the discharge of polluting gaseous and liquid effluents to the environment. Liquid effluents from the bleach plant are concentrated (e.g. evaporated), incinerated (e.g. gasified), leached, crystallized (e.g. freeze crystallized) then washed, and then fed to the plant chemical recovery loop. White liquor produced from the recovery boiler melt is fully oxidized and used in place of caustic in the bleach plant. Essentially all sulfuric acid, sulfur dioxide, caustic, and chlorine dioxide necessary for the pulp mill is produced from mill liquid effluents and gas waste streams, on site at the pulp mill. Typical bleaching sequences that can be used are DE.sub.op D.sub.n D, or AZE.sub.o PZP.

Apparatus for minimizing effluent discharges and recovering chemicals in

In minimizing effluents from a cellulose pulp mill, liquid effluents from a bleach plant are concentrated, and then incinerated to produce a residue including sodium, sulfate, and sodium chloride. This residue is distilled with sulfuric acid to produce gaseous hydrogen chloride and remaining residue, the HCl being used in chloride dioxide production for the bleach plant, while the remaining residue is passed to the recovery loop (e.g. recovery boiler). Sulfur containing gases from the non-condensible gas system may be combusted to produce gaseous sulfur dioxide, which is then converted to sulfuric acid, to distill the residue. Where a non-chlorine bleach plant is provided, the liquid effluents may be concentrated in evaporators and then passed directly to the recovery boiler. The liquid streams in the mill are managed by a cascade principle to reserve the cleanest water for only those processes where it is needed while minimizing its use where it is not necessary.

Zero discharge mill distillation, salt recovery, and water management

A pulp mill has zero or minimum liquid discharges. The large amounts of liquid that must be processed to achieve this result are handled utilizing a multiple effect evaporator provided with heat from a steam exhaust of a condensing type steam turbine. Super heated steam from the recovery and bark boilers is fed to the turbine to generate electricity for the production of bleaching chemical and other uses in the mill. Three or four steam exhausts having different composite temperature and pressure values are taken from the turbine and used where most suitable in the pulp mill. For evaporation of bleach plant effluent the steam taken from the turbine preferably has a pressure of about 1-3 psia and a temperature of about 120.degree.-140 .degree. F, and has no significant adverse affect on power generation.

Reducing pulp mill liquid discharge

Method for minimizing pulp mill effluents

A method and apparatus are provided for analyzing the elemental constituents of fluid streams in the cellulose pulp industry, such as liquid with dissolved solids for treatment of cellulose pulp or from the treatment of cellulose pulp, or liquid slurries including comminuted cellulose material. Continuous on-line elemental analyses are made of one or more such fluid streams, and at least the partial elemental make-up (either material, or of elements added for marking) of the streams determined. Then one or more processes for acting on the fluid streams are controlled to optimize the processes as a result of the analyses made. The invention is particularly useful in the continuous on-line analysis of black liquor utilizing prompt gamma neutron activation analysis, and controlling the operation of an evaporator or recovery boiler. The invention is also applicable to a paper pulp slurry in which case the carbon content of the slurry is analyzed to determine the precise solids consistency, and may employ NMR or 'H-MR.

Continuous elemental analysis of process flows

A method and apparatus for recovering black liquor chemicals and heat in a sulphate pulp process. The black liquor is concentrated in an evaporation plant, which includes a pressure heating reactor, after which the black liquor is gasified or combusted in a reactor for producing hot gases. The hot gases formed in the reactor are introduced into gas turbine power plant. The exhaust gases from the gas turbine are introduced into a waste heat boiler, where steam is generated for a steam turbine power plant. Secondary steam is led from the pressure heating reactor as injection steam into the gas turbine, to control inlet temperature.

Method for treating black liquor

A method of decreasing the viscosity and improving the evaporability of sulfate black liquor from the cellulose cook includes raising the temperature of the black liquor above the cooking temperature so as to split the macro-molecular lignin fraction contained in the liquor. The temperature of the black liquor is maintained at the raised level for 1 to 60 minutes, preferably for 1 to 5 minutes.

Method of decreasing black liquor viscosity

A method of concentrating sludges wherein liquor is heated under pressure indirectly with flue gases from the combustion of previously concentrated sludge, after which the sludge is caused to expand or subjected to reduced pressure which results in evaporation of water and concentration of the sludge to a dry-substance content of over 55%.

Method of concentrating sludges

A method of burning solid fuel having low melting point alkaline compositions, such as alkali metal salts, particularly lignite and salty brown coal. The fuel is introduced into the reaction chamber of a circulating fluidized bed reactor, and is mixed prior to introduction to the reaction chamber with a reactant material capable of reacting with the low melting point alkaline compositions of the fuel to produce high melting point alkali metal compounds during combustion. The temperature in the reaction chamber is kept below the melting point of the formed alkali metal compounds. The reactant material comprises silica oxide or a metal oxide, or hydroxide, of the group consisting of aluminum, calcium, magnesium, iron, titanium, and mixtures of two or more thereof. Kaolin is particularly effective, especially when the molar ratio of Al/(Na and K) is at least 1.0.

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Karhula, Finland

Erkki J Kiiskila