Abstract: The object of the present invention is a method in cooling medium circulation, whereby the recovery boiler comprises a furnace limited by wall tubes provided with cooling medium circulation and substantially horizontal floor tubes; a supply system for combustion air; and a supply system for black liquor, whereby a so-called smelt layer is formed in a combustion process on the floor composed of the floor tubes. At least in some of the floor tubes, at least on a section of their length, is arranged a longitudinal flow--particularly a spiral flow--for mixing the liquid and steam phases of the cooling medium.

Abstract: A method for adjusting the chlorine equilibrium in a sulphate cellulose process, wherein part of the chlorine contained in the cycle is separated and removed. In the method, strong odour gases from the sulphate cellulose process are introduced into a soda recovery boiler for burning so that chlorine contained in the liquor is in the form of hydrogen chloride (HCl) in the upper part of the soda recovery boiler and can subsequently be separated from the flue gases in a flue gas scrubber. The chlorine equilibrium is adjusted by removing part of the chlorine-containing washing solution.

Abstract: A method for burning secondary sludge in a recovery boiler, in which method secondary sludge is mixed with black liquor. According to the method, an alkali is added to the secondary sludge so as to obtain a mixture having a pH of over 7, whereafter the mixture of alkali and secondary sludge is heated to a temperature of over 80.degree. C. and kept at this temperature for over 30 minutes. Thereafter the heat treated mixture of alkali and secondary sludge is supplied to the thick end of a black liquor evaporation plant.

Abstract: A grate assembly for a fluidized bed boiler comprises a number of parallel sparge pipes or the like extending side-by-side in a substantially horizontal plane and provided with elements for supplying fluidizing air from within the sparge pipes or the like into a combustion chamber located above the grate assembly. The discharge of some of the fluidized bed materials is effected through an aperture system formed between the adjacent sparge pipes into a receiver unit fitted below the grate assembly. The sparge pipes are provided with a cooling medium circulation by means of a duct assembly.

Abstract: The invention relates to a method of adjusting the sulphur balance of a sulphate cellulose plant, in which method black liquor is concentrated and heat treated by keeping it at a temperature higher than the cooking temperature for a certain time period to separate the sulphur compounds contained in the black liquor as gaseous sulphur compounds therefrom in the last evaporation stage of a series of evaporation stages.

Abstract: Method of reducing scaling of heat transfer surfaces in an evaporation plant of a sulphate cellulose mill when sulphate cellulose is manufactured. In the method, ash to be fed into black liquor is mixed thereto after soap separation when the dry solids content of the black liquor is so low that sodium sulphate and other soluble salts contained in the ash dissolve in the black liquor completely.

Abstract: Process for removing nitrogen oxides from the flue gases of a soda recovery boiler of a pulp mill. In the method, to the flue gases of the soda recovery boiler is at first fed an oxidizing agent, such as chlorine dioxide or ozone, which oxidizes nitrogen oxide to nitrogen dioxide. Subsequently, the flue gases are led into a flue gas scrubber, in which a reagent coming from the circulation of chemicals of the pulp mill is injected into the flue gases, which reagent brought into contact with the nitrogen dioxide reduces the nitrogen dioxide to nitrogen. The flue gas containing nitrogen is led out of the scrubber and the oxidized reagent is led back to the circulation of chemicals of the pulp mill.

Abstract: An evaporator operating on falling film principle, has a shell (1) with a system (2) of evaporating tubes therein, whereby a liquid to be concentrated is fed on the outer surface of the evaporating tube system (2) and vapor is led to flow inside the tubes of the evaporating tube system (2). The evaporating tube system (2) is formed of evaporating elements, each evaporating element being formed of evaporating tubes (9) substantially on the same level. The upper ends of the tubes are connected to a common collecting chamber (8) and the lower end, respectively, to a common collecting chamber (10) in such a manner that there is a connection between both collecting chambers (8, 10) through each tube (9) between them, due to which the collecting chambers (8) of the upper end of the evaporating elements are interconnected through the upper connecting chamber (12), and respectively, the collecting chambers (10) of the lower end are interconnected through the connecting chamber (13) of the lower end.

Abstract: A method for adjusting the sulphur/sodium ratio in a soda recovery boiler when strong sulphurous odour gases are burned therein. According to the method, sodium is introduced into the soda recovery boiler in an amount proportional to the amount of sulphur either as sodium hydroxide, sodium carbonate compounds or soap, whereby the sodium and sulphur react, forming sodium sulphate, which can be removed from the flue gases together with fly ash.

Abstract: An air nozzle (3) mounted in the wall of a recovery boiler for supplying air from a supply duct (4) into the recovery boiler. The air nozzle (3) comprises a nozzle duct (7) attached to the wall of the recovery boiler and a separate nozzle part (3a) insertable into the nozzle duct in its longitudinal direction, air being supplied into the recovery boiler through a duct provided in the nozzle part (3a).

Abstract: A single-drum recovery boiler comprising a superheater (2), boiler bank elements (3a) forming a boiler bank, and elements (3b) forming an economizer. In the recovery boiler, a plurality of boiler bank elements (3a) and economizer elements (3b) are disposed alternately so that a boiler bank--economizer unit (3) is achieved where the ratio between the boiler bank elements and the economizer elements is optimized in relation to the operating conditions of the boiler.

Abstract: The invention relates to a process for cooling gases using a circulating fluidized bed technique, wherein gas is conveyed through a fluidized bed formed by circulating fluidized bed material so that part of the circulating fluidized bed material is driven along with the gas flow and whereby the circulating fluidized bed material entrained in the gas flow is separated from the gas flow and returned into the fluidized bed, and wherein at least part of the cooling is carried out by cooling the circulating fluidized bed material stream to be returned. The process is characterized in that substantially the entire cooling is realized by cooling the circulating fluidized bed material stream to be returned in a heat exchanger (10) separate from the gas flow duct, in which event the cooling of the gas stream is effected by means of the circulating fluidized bed material stream returned to the fluidized bed and having a temperature lower than that of the fluidized bed.

Abstract: The invention relates to a combustion unit, which for effecting a circulating mass process comprises a reactor chamber, whose lower part is, for formation of a fluidized bed, fitted with a grate structure (10), at least one particle separator with means for purifying the combustion gas containing solid material, formed in the fluidized bed, from said solid material, and a return duct (6a) for returning the solid material particularly to the fluidized bed. A gas lock structure (KL) as an extension of the return duct (6a) prevents the gas flow to the opposite direction and comprises a combination formed by a closed bottom structure (14), a cover structure (11) placed above the bottom structure (14) and having openings (12a), an interspace (13) formed between the bottom structure (14) and the cover structure (11), and openings (15a) placed in the wall of the return duct (6a) between the bottom structure (14) and the cover structure (11), as seen in vertical direction, and connected with the interspace ( 13).

Abstract: Process and apparatus for removal of sulfur oxides from flue gases.In the process, a NaOH solution is injected into flue gases containing calcium oxide so that the formed reaction products are discharged from the reactor in a dry dust-like form together with the flue gases, whereafter the solids present in the flue gases are separated from the flue gases, mixed with water and sodium so as to form a sodium hydroxide solution wherefrom the other reaction products in solid form can be removed, the sodium hydroxide solution being returned to the flue gases.The apparatus comprises a desulfurization reactor (3) wherein a sodium hydroxide solution is injected into the flue gases, and an electrostatic precipitator (5) wherein the dust-like solids are separated from the flue gases.

Abstract: The invention relates to a process for cooling gases using a circulating fluidized bed technique, wherein gas is conveyed through a fluidized bed formed by circulating fluidized bed material so that part of the circulating fluidized bed material is driven along with the gas flow and whereby the circulating fluidized bed material entrained in the gas flow is separated from the gas flow and returned into the fluidized bed, and wherein at least part of the cooling is carried out by cooling the circulating fluidized bed material stream to be returned. The process is characterized in that substantially the entire cooling is realized by cooling the circulating fluidized bed material stream to be returned in a heat exchanger (10) separate from the gas flow duct, in which event the cooling of the gas stream is effected by means of the circulating fluidized bed material stream returned to the fluidized bed and having a temperature lower than that of the fluidized bed.

Abstract: The invention relates to a method and an equipment for the recovery of energy and chemicals in a sulphate process, wherein black liquor is passed into a gasification reactor (3) in which it is gasified at a pressure above the atmospheric pressure in the presence of an amount of oxygen smaller than the stoichiometric amount, whereby inorganic compounds are recovered as liquid-phase compounds useable in the present pulping process, and the energy of the organic compounds of black liquor is bound mainly to the chemical compounds of the gas phase. Gases formed in the gasification, containing sodium compounds, are passed into a particle cooler (4), in which the compounds are brought into solid state. Gases cooled in the particle cooler (4) are purified by a filter (5) and then passed into a gas turbine (7).

Abstract: Combustion unit which for attaining a circulation process comprises a reactor chamber (1) and a particle separator (6) which is provided with two casings (7, 8) and which is placed inside the reactor chamber to the upper part thereof. At least the first i.e. the outer casing (7) of the particle separator (6) is arranged to form a heat transfer surface. The roof structure (1a) of the reactor chamber (1) is attached to the outer casing (8).

Abstract: A combustion unit for a circulation process comprises a reactor chamber and at least one particle separator placed inside the reactor chamber in the upper part thereof. At least the first outer casing of the particle separator is arranged to form a heat transfer surface. A flue gas inlet into the first outer casing is arranged to extend for the entire circumference of the casing.