Method for controlling a recovery boiler

Patent metadata

Field	Value
Publication number	US-10655849-B2
Application number	US-201815997140-A
Country	US
Kind code	B2
Filing date	Jun 4, 2018
Priority date	Jun 20, 2017
Publication date	May 19, 2020
Grant date	May 19, 2020

Abstract

The method in a recovery boiler comprises estimating the first melting temperature T 0 of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) content of the fly ash; measuring or estimating the temperature T ss of superheated steam; evaluating a temperature difference T D1 between the first melting temperature T 0 and the temperature T ss of the superheated steam, the temperature difference T D1 providing an estimate of the risk of corrosion; and selecting a control action for influencing the temperature difference T D1 . Alternatively or additionally, the method comprises estimating the sticky temperature T STK of the fly ash depositing on heat transfer surfaces, the estimating being based on potassium (K) and chlorine (Cl) contents of the fly ash; measuring or estimating the temperature T FG of the flue gases; evaluating a temperature difference T D2 between the sticky temperature T STK and the temperature T FG of the flue gases; the temperature difference T D2 providing an estimate of the risk of plugging; and selecting a control action for influencing the temperature difference T D2 .

First claim

The invention claimed is:

1. A method for controlling a recovery boiler, the recovery boiler comprising a furnace for black liquor combustion, a superheater area having one or more superheaters and a boiler bank recovering heat from a stream of flue gases coming from the furnace; the method comprising:
estimating the sticky temperature T STK of the fly ash depositing on heat transfer surfaces of the superheater area and the boiler bank, the estimating being based on potassium (K) and chlorine (Cl) contents of the fly ash;
measuring or estimating the temperature T FG of the flue gases flowing at the boiler bank, or the superheater area or one or more superheaters of the superheaters;
evaluating a temperature difference T D2 between the sticky temperature T STK and the temperature T FG of the flue gases; the temperature difference T D2 providing an estimate of the risk of plugging at the boiler bank, or the superheater area or said one or more superheaters; and
selecting a control action for performing control of the recovery boiler and influencing the temperature difference T D2 .

2. The method according to claim 1 , further comprising:
comparing the temperature difference T D2 to a first predetermined temperature difference or a first predetermined temperature range; and
selecting the control action for performing control of the recovery boiler in such a way that the temperature difference T D2 increases when the temperature difference T D2 is smaller than the first predetermined temperature difference or below the first predetermined temperature range.

3. The method according to claim 2 , further comprising:
comparing the temperature difference T D2 to a second predetermined temperature difference or a second predetermined temperature range; and
selecting the control action for performing control of the recovery boiler such that the temperature difference T D2 decreases when the temperature difference T D2 is bigger that the second predetermined temperature difference or above the second predetermined temperature range.

4. The method according to claim 1 , wherein the control action is:
controlling the proportion of fly ash being purged or being fed to an ash treating process adapted to remove potassium and/or chlorine from the fly ash, or controlling both of them;
decreasing the proportion of the fly ash being purged or treated when the temperature difference T D2 increases; and
increasing the proportion of the fly ash being purged or treated when the temperature difference T D2 decreases.

5. The method according to claim 1 , wherein the control action is controlling the timing and procedure of cleaning actions related to the heat transfer surfaces of the superheater area, or the heat transfer surfaces of said one or more superheaters, or the heat transfer surfaces of the boiler bank.

6. The method according to claim 1 , wherein:
the recovery boiler further comprises at least one economizer recovering heat from a stream of flue gases coming from the furnace and an electrostatic precipitator collecting fly ash from the stream of flue gases; and
the method further comprises measuring or determining the potassium and chlorine contents of the fly ash collected in the electrostatic precipitator, or caught in the boiler bank, or caught in the economizer, or carried by the stream of flue gases.

7. The method according to claim 1 , the method further comprising measuring or estimating the temperature T FG of the flue gases upstream of the boiler bank or upstream of a superheater of the superheaters.

8. The method according to claim 1 , wherein the estimation of the sticky temperature T STK is based on the potassium and chlorine contents and one or more of the following: the sodium content, carbonates content or the sulfates content of the fly ash.

9. The method according to claim 4 , wherein the control action further comprises:
collecting fly ash from the stream of flue gases with an ash collecting and conveying system; and
removing potassium and/or chlorine from collected fly ash in the ash treating process and recirculating treated fly ash to black liquor before feeding the black liquor to the furnace.

10. The method according to claim 4 , wherein the control action further comprises:
collecting fly ash from the stream of flue gases with an ash collecting and conveying system; and
changing, by means of the purging, the amount of fly ash recirculated back to black liquor before feeding the black liquor to the furnace.

Assignees

• Valmet Automation Oy

Inventors

• Mansikkasalo Jarmo
• Koskinen Jukka

Classifications

• D21C11/12 Primary

  Combustion of pulp liquors · CPC title

• D21C11/066 Primary

  Separation of solid compounds from these gases; further treatment of recovered products · CPC title

• F23G7/04 Primary

  of waste liquors, e.g. sulfite liquors · CPC title

• F23J15/022

  for removing solid particulate material from the gasflow · CPC title

• D21C11/106

  Prevention of incrustations on heating surfaces during the concentration, e.g. by elimination of the scale-forming substances contained in the liquors · CPC title