Method and a system for quality optimization of green liquor

Patent metadata

Field	Value
Publication number	US-10385513-B2
Application number	US-201715707676-A
Country	US
Kind code	B2
Filing date	Sep 18, 2017
Priority date	Sep 16, 2016
Publication date	Aug 20, 2019
Grant date	Aug 20, 2019

Abstract

A method for optimizing reduction and content of total titratable alkali of green liquor of a recovery boiler. The method comprises producing green liquor in a dissolving tank by conveying smelt and weak white liquor into the dissolving tank and measuring at least the contents of sodium sulphate, sodium hydroxide, sodium sulphide, and sodium carbonate of the green liquor. The method comprises controlling at least a process parameter of a recovery boiler to maximize the reduction of the recovery boiler and controlling the flow of the weak white liquor into the dissolving tank to optimize the content of total titratable alkali of the green liquor. In addition, a system for producing green liquor with optimized reduction and content of total titratable alkali. The system comprises a first sensor arrangement, a first and a second regulator, and a processing unit arrangement configured to perform the method.

First claim

The invention claimed is:

1. A method for optimizing a reduction and a content of total titratable alkali of a green liquor of a recovery boiler, the method comprising:
producing the green liquor by dissolving a smelt from the recovery boiler in a dissolving tank by conveying a weak white liquor into the dissolving tank,
measuring at least
a content of sodium sulphate (Na 2 SO 4 ) of the green liquor,
a content of sodium hydroxide (NaOH) of the green liquor,
a content of sodium sulphide (Na 2 S) of the green liquor, and
a content of sodium carbonate (Na 2 CO 3 ) of the green liquor,

controlling at least one of a temperature and an oxygen content within the recovery boiler by using the measured content of sodium sulphate (Na 2 SO 4 ) and the measured content of sodium sulphide (Na 2 S) to maximize the reduction in the recovery boiler, and
at a first instance of time, controlling the flow of the weak white liquor into the dissolving tank by using the measured content of sodium sulphate (Na 2 SO 4 ), the measured content of sodium hydroxide (NaOH), the measured content of sodium sulphide (Na 2 S), and the measured content of sodium carbonate (Na 2 CO 3 ) to optimize the content of total titratable alkali of the green liquor.

2. The method of claim 1 , further comprising:
determining a melting temperature for a char bed of the recovery boiler,
measuring a temperature of the char bed, and
controlling the at least one of the temperature and the oxygen content within the recovery boiler in such a way that a flow of the smelt is continuous.

3. The method of claim 2 , further comprising:
measuring at least the content of sodium sulphate (Na 2 SO 4 ) of the weak white liquor, the content of sodium hydroxide (NaOH) of the weak white liquor, the content of sodium sulphide (Na 2 S) of the weak white liquor, and the content of sodium carbonate (Na 2 CO 3 ) of the weak white liquor,
determining the flow rate of a black liquor into a furnace of the recovery boiler,
determining the flow rate of the green liquor and the flow rate of the weak white liquor, and
measuring contents of chlorine (Cl) and potassium (K) from ash produced by the recovery boiler,
wherein the determining of the melting temperature for the char bed of the recovery boiler uses at least
the measured contents of chlorine and potassium, as measured from the ash,
the measured contents of sodium sulphate (Na 2 SO 4 ), sodium hydroxide (NaOH), sodium sulphide (Na 2 S), and sodium carbonate (Na 2 CO 3 ) of the green liquor,
the measured contents of sodium sulphate (Na 2 SO 4 ), sodium hydroxide (NaOH), sodium sulphide (Na 2 S), and sodium carbonate (Na 2 CO 3 ) of the weak white liquor,
the determined flow rate of the black liquor into the furnace of the recovery boiler, and
the determined flow rate of the green liquor and the flow rate of the weak white liquor.

4. The method of claim 3 , further comprising determining, in units of mass per time: (i) the flow rate of the black liquor into the furnace, (ii) the flow rate of the green liquor, and (iii) the flow rate of the weak white liquor, by measuring: (a) the flow rate of the green liquor in units of volume per time, (b) the flow rate of the weak white liquor in units of volume per time, (c) the density of the green liquor, and (d) the density of the weak white liquor.

5. The method of claim 1 , wherein the at least one of the temperature and the oxygen content within the recovery boiler is controlled by controlling at least one process parameter of the recovery boiler selected from the group consisting of:
a flow rate of combustion air into the recovery boiler,
a distribution of the combustion air in the recovery boiler,
a pressure of the combustion air,
a flow velocity of the combustion air,
a pressure of a concentrated black liquor, which is fed to a furnace of the recovery boiler,
a temperature of the concentrated black liquor,
a flow velocity of the concentrated black liquor, and
a size of an orifice of a nozzle used to feed a black liquor into the furnace.

6. The method of claim 1 , further comprising:
measuring a temperature of the green liquor,
determining, using: (i) the measured temperature of the green liquor, (ii) the measured content of sodium carbonate (Na 2 CO 3 ) of the green liquor, (iii) the measured content of sodium sulphate (Na 2 SO 4 ) of the green liquor, (iv) the measured content of sodium hydroxide (NaOH) of the green liquor, and (v) the measured content of sodium sulphide (Na 2 S) of the green liquor:
a maximum allowable value for a quantity indicative of at least an amount of a pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) forming component in the green liquor on the condition that a solubility limit of pirssonite is not exceeded, and
a value of the quantity indicative of at least an amount of the pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) forming component in the green liquor, and

controlling the flow of the weak white liquor into the dissolving tank by using:
the determined maximum allowable value for the quantity indicative of at least an amount of a pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) forming component in the green liquor on the condition that the solubility limit of pirssonite is not exceeded, and
the determined value of the quantity indicative of at least an amount of the pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) forming component in the green liquor, in such a way that

the content of total titratable alkali of the green liquor is maximized on the condition that solid pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) is not formed in the green liquor.

7. The method of claim 6 , further comprising:
determining, using at least the measured temperature of the green liquor, the measured content of sodium carbonate (Na 2 CO 3 ) of the green liquor, and information on the solubility of pirssonite in the green liquor, a theoretical maximum value for the quantity indicative of at least an amount of a component of pirssonite on the condition that solid pirssonite (Na 2 Ca(CO 3 ) 2 .2H 2 O) is not formed in the green liquor,
determining a safety margin for the quantity indicative of at least an amount of a component of pirssonite, and
controlling the flow of the weak white liquor into the dissolving tank by optimizing the value of the quantity indicative of at least an amount of a component of pirssonite towards a target value that is calculated by subtracting the determined safety margin from the determined theoretical maximum value.

8. The method of claim 1 , wherein:
the content of sodium sulphate (Na 2 SO 4 ) of the green liquor, is measured on-line at a second instance of time, and the second instance of time is at most 4 hours earlier than the first instance of time.

9. The method of claim 8 , wherein the second instance of time is at most 1 hour earlier than the first instance of time.

10. The method of claim 1 , further comprising:
measuring, at a second or third instance of time, at least one of:
the content of sodium sulphate (Na 2 SO 4 ) of the green liquor,
the content of sodium hydroxide (NaOH) of the green liquor,
the content of sodium sulphide (Na 2 S) of the green liquor, and
the content of sodium carbonate (Na 2 CO 3 ) of the green liquor,

at a fourth instance of time, which is after the second or third instance of time and before the first instance of time, measuring a density of the green liquor on-line, and
[A]
determining a target value for the density of green liquor using the measured temperature, the measured content of sodium carbonate (Na 2 CO 3 ), the measured content of sodium sulphate (Na 2 SO 4 ), the measured content of sodium hydroxide (NaOH), and the measured content of sodium sulphide (Na 2 S) of the green liquor,

Assignees

• Valmet Automation Oy

Inventors

• Koskinen Jukka A
• Leskinen Mikko
• Mansikkasalo Jarmo

Classifications

• D21C11/12

  Combustion of pulp liquors · CPC title

• D21C11/10

  Concentrating spent liquor by evaporation (evaporators B01D) · CPC title

• D21H17/66 Primary

  Salts, e.g. alums · CPC title

• C01D7/00

  Carbonates of sodium, potassium or alkali metals in general · CPC title

• D21C11/122

  Treatment, e.g. dissolution, of the smelt · CPC title