Method and a system for quality optimization of green liquor

Patent metadata

Field	Value
Publication number	US-2018080173-A1
Application number	US-201715707676-A
Country	US
Kind code	A1
Filing date	Sep 18, 2017
Priority date	Sep 16, 2016
Publication date	Mar 22, 2018
Grant date	—

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

1 - 18 . (canceled)

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

20 . The method of the claim 1 , comprising
determining a melting temperature for the char bed of the recovery boiler, measuring the temperature of the char bed, and controlling at least a process parameter of the recovery boiler in such a way that the flow of smelt is continuous;
preferably the method comprises
measuring at least
the content of sodium sulphate (Na 2 SO 4 ),
the content of sodium hydroxide (NaOH),
the content of sodium sulphide (Na 2 S), and
the content of sodium carbonate (Na 2 CO 3 )

of the weak white liquor,
determining the flow rate of black liquor into the furnace of the recovery boiler,
determining the flow rate of green liquor and the flow rate of weak white liquor,
measuring the content of chlorine (Cl) and potassium (K) from the ash produced by the recovery boiler, and
determining the melting temperature of the char bed of the recovery boiler by using at least
the content of chlorine and potassium, as measured from the ash and
the contents of sodium sulphate (Na 2 SO 4 ), sodium hydroxide (NaOH), sodium sulphide (Na 2 S), and sodium carbonate (Na 2 CO 3 ) measured from the green liquor,
the contents of sodium sulphate (Na 2 SO 4 ), sodium hydroxide (NaOH), sodium sulphide (Na 2 S), and sodium carbonate (Na 2 CO 3 ) measured from the weak white liquor,
the flow rate of black liquor into the furnace of the recovery boiler, and
the flow rate of green liquor and flow rate of weak white liquor;

preferably, the method further comprises
determining the flow rate of black liquor into the furnace, the flow rate of green liquor and the flow rate of weak white liquor in units of mass per time, for example by measuring
the flow rate of green liquor in units of volume per time,
the flow rate of weak white liquor in units of volume per time,
the density of green liquor, and
the density of weak white liquor.

21 . The method of claim 19 , wherein the process parameter of the recovery boiler is selected from the group comprising
the flow rate of combustion air into the recovery boiler, the distribution of combustion air in the recovery boiler, the pressure of combustion air, the flow velocity of combustion air, the pressure of the concentrated black liquor, which is fed to the furnace, the temperature of the concentrated black liquor, the flow velocity of the concentrated black liquor, and size of an orifice of a nozzle used to feed black liquor into the furnace.

22 . The method of claim 19 comprising
measuring the temperature of the green liquor,
determining, 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
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 the 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 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 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.

23 . The method of claim 22 , 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 safety margin from the theoretical maximum value.

24 . The method of claim 19 , wherein
the content of sodium sulphate (Na 2 SO 4 ) of the green liquor, is measured on-line at a second instance of time, wherein the second instance of time is at most 4 hours earlier than the first instance of time;
preferably
the second instance of time is at most 1 hour or at most 30 minutes, or at most 10 minutes earlier than the first instance of time.

25 . The method of claim 19 , wherein 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 is measured at a third or the second instance of time,
the method comprising
after the second or third instance of time and before the first instance of time, at a fourth instance of time, measuring the 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,
controlling the flow of the weak white liquor into the dissolving tank by using the measured density of the green liquor and the target value for the density of green liquor or

[B]
determining 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 using the measured density of the green liquor.

26 . The method of claim 19 , comprising
determining a value indicative of a change of flow rate of the smelt from the recovery boiler into the dissolving tank an

Assignees

• Valmet Automation Oy

Inventors

• Koskinen Jukka A
• Leskinen Mikko
• Mansikkasalo Jarmo

Classifications

• D21C11/122

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

• D21C11/0064 Primary

  Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor · CPC title

• D21H17/66 Primary

  Salts, e.g. alums · CPC title

• C01D5/00

  Sulfates or sulfites of sodium, potassium or alkali metals in general {(sulfites in general C01B17/62)} · CPC title

• C01D1/04

  Hydroxides · CPC title