Gas separation: apparatus – With gas and liquid contact apparatus – Liquid bath or reservoir for contact
Reexamination Certificate
1999-03-08
2001-05-29
Smith, Duane S. (Department: 1724)
Gas separation: apparatus
With gas and liquid contact apparatus
Liquid bath or reservoir for contact
C095S226000, C096S351000
Reexamination Certificate
active
06238468
ABSTRACT:
1. Technical Field
The present invention provides a novel process for recovering chemicals and energy from a spent liquor obtained from production of pulp. The present invention also provides a novel recovery installation for recovering chemicals and energy from a spent liquor obtained from the production of pulp.
2. Background of the Invention
When producing paper pulp by the kraft method, a spent liquor is obtained, which is generally called black liquor. The black liquor contains organic material and the residual chemicals from digesting the fibrous raw material. This black liquor is generally evaporated and conveyed to a separate processing stage for recovery of the energy content of the organic material and also for recovery of the cooking chemicals. The cooking chemicals are usually recovered in a liquor, called green liquor. The well known Tomlinson process has been the commercially predominant method for this recovery of energy and chemicals. However, a disadvantage of the Tomlinson process is that it requires very large combustion furnaces which are complicated from the technical and operational points of view.
Swedish Patent SE-C-448 173 describes a more modern process which, in addition to considerably simplifying the necessary process equipment, achieves improved recovery of both energy and chemicals. This process is based on a pyrolysis reaction in which the black liquor is gasified in a Chemrec® reactor. The process produces an energy-rich gas principally comprising carbon monoxide, carbon dioxide, methane, hydrogen and hydrogen sulphide. Inorganic chemicals are also produced in the form of small drops of smelt, principally comprising sodium carbonate, sodium hydroxide and sodium sulphide. The resulting mixture of gas and drops of smelt is quickly cooled in a first stage by direct contact with a cooling liquid. Green liquor is formed when the smelt chemicals and the hydrogen sulphide are dissolved in the cooling liquid. The gas is thereafter washed in a second stage in a scrubber type gas washer. The gas is then used as fuel for generating steam and/or electrical power. The physical thermal value of the gas can also be used when the gas is cooled from the gasification temperature to the saturation temperature for producing steam at the selected pressure. The green liquor which is formed is conveyed to a causticizing stage for production of white liquor.
SE-B-468 600 discloses a process for producing white liquor of high sulphidity (a high proportion of sodium hydrogen sulphide in relation to the proportion of sodium hydroxide) directly from the gasification reactor and without any need for causticizing. In this process, hydrogen sulphide is recovered from the gaseous phase exhausted in the Chemrec® reactor and is returned to the reactor in order to be present during the thermal decomposition of the spent liquor. In this way, such a high partial pressure of hydrogen sulphide is established in the gasification stage that the following equilibrium reaction (a)
Na
2
CO
3
+H
2
S→Na
2
S+CO
2
+H
2
O (a)
is displaced so far to the right that the formation of Na
2
CO
3
is substantially suppressed. The Na
2
S formed is dissociated to form NaOH and NaHS.
The recovery of hydrogen sulphide from the gaseous phase takes place by passing the gas through a gas washer containing an external absorption chemical, for example N-methyl-pyrrolidone or methyidiethylamine, for selective and regernative absorption of the H
2
S present in the gas. The requirement for such an external chemical represents a significant disadvantage of this process and additionally makes it necessary to provide an undesirable regeneration stage for driving off the hydrogen sulphide from the absorption chemical.
Swedish Patent SE-C465 039 describes a method which has the object of producing a cooking liquor having a high sulphidity. Material containing sulphur and/or material containing sulphur and sodium, which generally occur in the pulp mill, are conveyed to a reactor together with the black liquor.
A general disadvantge of previously known recovery techniques is that the recovery of chemicals has been governed by the available process technology. For example, the sulphidity of the white liquor has been adapted to the requirements of the recovery boiler and not to the requirements of the cooking department. Nor has there been any commercially feasible technique for producing liquors having differing properties for different uses in the pulp mill.
SUMMARY OF THE INVENTION
An objective of the present invention is to recover valuable chemicals from a spent liquor in a flexible process that is capable of producing multiple liquors containing different concentrations of the recovered valuable chemicals.
Another objective of the present invention is to provide a flexible process by which the sulphidity of the white liquor can be easily adjusted to provide white liquors having different levels of sulphidity. In this manner, white liquors can be easily tailored for different uses in the pulp mill.
A further objective of the present invention is to provide a recovery installation that is adapted to produce liquors having different concentrations of recovered valuable chemicals, including different levels of sulphidity.
A further objective of the present invention is to provide a method and recovery installation for producing white liquors having different concentration of recovered chemicals in which the need for causticizing is significantly reduced or even substantially avoided.
The above objectives and other objectives can be surprisingly be obtained by the following. The invention provides a process for producing liquors containing different concentrations of recovered process chemicals or combustion gasses containing different concentrations of process chemicals from a spent liquor obtained from the production of pulp, said method comprising the steps of:
gasifying a portion of the spent liquor in a first reactor under a first set of reaction conditions to produce a first smelt and a first combustion gas having a first concentration of process chemicals;
dissolving said first smelt in a first aqueous liquid to produce a first liquor having a first concentration of process chemicals;
gasifying a portion of the spent liquor in a second reactor under a second set of reaction conditions to produce a second smelt and a second combustion gas having a second concentration of process chemicals;
dissolving said second smelt in a second aqueous liquid to produce a second liquor having a second concentration of process chemicals, wherein said first set of reaction conditions is selected to be different from said second set of reaction conditions such that at least one of said first concentration of process chemicals in said first combustion gas or said first liquor being different from said second concentration of process chemicals in said second combustion gas or said second liquor.
The invention also provides process for producing liquors containing different concentrations of process chemicals or combustion gasses containing different concentrations of process chemicals from a spent liquor obtained from the production of pulp, said method comprising the steps of:
gasifying a portion of the spent liquor in a first reactor at a first pressure and first temperature to produce a first smelt and a first combustion gas having a first concentration of recovered process chemicals;
dissolving said first smelt in a first aqueous liquid to produce a first liquor having a first concentration of process chemicals;
gasifying a portion of the spent liquor in a second reactor at a second pressure and second temperature to produce a second smelt and a second combustion gas having a second concentration of process chemicals;
dissolving said second smelt in a second aqueous liquid to produce a second liquor having a second concentration of process chemicals, wherein at least one of said second pressure or said second temperature is selected to be different from said first pressure or said first temperatu
Kvaerner Pulping AB
Manelli Denison & Selter PLLC
Melcher Jeffrey S.
Smith Duane S.
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