Title of Invention	"A PROCESS FOR RECOVERING SPENT CHEMICALS FROM BLACK LIQUOR DURING PAPER MAKING PROCESS AND INTEGRATED THEREOF"
Abstract	This invention relates to A process for recovering spent chemicals from black liquor during paper making process comprising the steps of -feeding electrostatic precipitator ash (9) from electrical precipitator rotary feeder to a common chemical ash tank (26); thoroughly mixing electrostatic precipitator ash in said common chemical ash tank with incoming heavy black liquor (7) originated in multiple effect evaporator; adding salt cake (14) in said common chemical ash tank (26) and agitating; feeding into said common chemical ash tank, economizer bottom ash; (!5); mixing thoroughly said electrostatic precipitator ash (EP ash)and salt cake (14) with black liquor in said common chemical ash tank; pumping (2?) mixed black liquor from said common chemical ash tank to a secondary black liquor heater (29) and finally allowing the black liquor to pass to a furnace (30) for recovery of the spent chemicals from the black liquor. This invention relates also to an integrated plant for carrying out the above process.

Title of Invention

"A PROCESS FOR RECOVERING SPENT CHEMICALS FROM BLACK LIQUOR DURING PAPER MAKING PROCESS AND INTEGRATED THEREOF"

Abstract

This invention relates to A process for recovering spent chemicals from black liquor during paper making process comprising the steps of -feeding electrostatic precipitator ash (9) from electrical precipitator rotary feeder to a common chemical ash tank (26); thoroughly mixing electrostatic precipitator ash in said common chemical ash tank with incoming heavy black liquor (7) originated in multiple effect evaporator; adding salt cake (14) in said common chemical ash tank (26) and agitating; feeding into said common chemical ash tank, economizer bottom ash; (!5); mixing thoroughly said electrostatic precipitator ash (EP ash)and salt cake (14) with black liquor in said common chemical ash tank; pumping (2?) mixed black liquor from said common chemical ash tank to a secondary black liquor heater (29) and finally allowing the black liquor to pass to a furnace (30) for recovery of the spent chemicals from the black liquor. This invention relates also to an integrated plant for carrying out the above process.

Full Text	This invention relates to a process of recovering spent chein teals from bla€ liquor during paper making process. During the process of making paper in pulp mill, recovery boiler provides a means of recovering spent chemical from black liquor that results from the digesting process and is utilized as a steam generator by burning out the organic matters presents i» black liquor. The heavy black liquor leaving the Multiple Effect Evaporator (MEE) in a pulp mil! is pumped to the black liquor storage tank of the chemical recovery unit (CRU) From the black liquor storage tank, heavy black liquor is transferred to EP ash tank, where it is mixed with chemical ash obtained from electrostatic Prectpitators (EP). The liquor is then pumped from EP ash tank by EP ash pumps to Salt Cake Mixing Tank (SCMT). In SCMT the make-up chemical viz Na2S04 (salt cake) is added. From SCMT, black liquor is passed through black liquor heaters and is pumped to the black liquor spray guns through which it is finaly introduced into the furnace where it is burned. During the burning process, the ash in black liquor is liberated and reduced and, in molten state, drained from the furnace bottom through smelt spouts to Main Dissolving Tank (MDT). Since the molten ash is water soluble it is conveniently quenched and dissolved in MDT. The dissolved smelt in water is then pumped to a causticizer for further processing and recycling. In dry Electrostatic Precipitator (EP) ash return system, the EP ash from EP rotary feeders outlet is transferred to the salt cake mixing tank by one set of conveyors. Each economizer bank is having a chain conveyor, which runs across the width of the economizer bank and collects the ash settling at the economizer bottom. This ash is fed through a rotary feeder to the common EP ash conveyor which transports both the economizer bottom ash and the EP ash to the SCMT. In SCMT the salt cake is added to the black liquor to compensate the chemical losses in the paper making process. The incoming black liquor from MEE is thoroughly mixed with the salt cake and the ash in SCMT by agitators. SCMT is provided with black liquor heaters to maintain the black liquor temperature required for Heavy Black Liquor (HBL) pumps. The black liquor from SCMT is pumped by HBL pumps to the furnace. A secondary black liuor heater is provided in black liquor line to maintain the black liquor temperature for firing. In wet EP ash return system, the EP ash from EP rotary feeders outlet is transported by a pair of conveyors to the EP ash tanks. The EP ash is thoroughly mixed in EP ash tank with the incoming black liquor from MEE. Then the black liquor is pumped by EP ash pumps to SCMT through the flowbox. Each economizer bank is having a bottom chain conveyor, which runs across the width of the economizer bank and collects the ash settling at the economizer bottom. This ash is fed through a rotary feeder to the common economizer bottom ash conveyor to the SCMT. In SCMT the salt cake is added to the black liquor. The incoming black liquor from EP ash tank is thoroughly mixed with the salt cake in SCMT by agitators. SCMT is provided with a black liquor heater to maintain the black liquor temperature required for HBL pumps. The black liquor from SCMT is pumped by HBL pumps to the furnace. A secondary black liquor heater is provided in black liquor line to maintain the black liquor temperature for firing. One of the objects of the present invention is to dispense with some of the essential units of the conventional system for recovery of spent chemicals from black liquor. Another object of the present invention is to use only a common chemical ash tank for mixing of ash from EP and economizer and make up salt-cake instead of separate EP ash tanks and salt cake mixing tanks. This eliminates a set of tanks, associated pumps and flow box. A still further object of the present invention is to accommodate the improved system with a much lesser floow space. A further object of this invention is to economize the whole system and the process, by providing lesser means and fewer steps in recovering, in the pulp mill, the spent chemical from black liquor. The other objects of the present invention can be clearly understood from the following paragraphs of the present specification. According to this invention there is provided a process for recovering spent chemicals from black liquor during paper making process comprising the steps of - a) feeding electrostatic precipitator ash from electrical precipitator rotary feeder to a common chemical ash tank; b) thoroughly mixing electrostatic precipitator ash in said common chemical ash tank with incoming heavy black liquor originated in multiple effect evaporator; c) adding salt cake in said common chemical ash tank and agitating; d) feeding into said common chemical ash tank, economizer bottom ash; e) mixing thoroughly said electrostatic precipitator ash and salt cake with black liquor in said common chemical ash tank; f) pumping mixed black liquor from said common chemical ash tank to a secondary black liquor heater, and finally g) allowing the black liquor to pass to a furnace for recovery of the spent chemicals from the black liquor. In the above process of recovering spent chemicals from black liquor the electrostatic precipitator ash is transported through a rotary feeder to the common chemical ash tank by a pair of conveyors. The present system for carrying out a process for recovering spent chemicals from black liquor system which comprises an electrostatic precipitator ash tank, a salt cake mixing tank, a secondary black liquor heater and a furnace, said electrostatic precipitator ash tank being connected to salt cake mixing tank through an electrostatic precipitator ash pump and a flow box for transporting electrostatic precipitator ash and mixing it with black liquor into said flow box, a high powered pump being adapted and located to connect said salt cake mixing tank with said secondary black liquor heater for maintaining regular flow of black liquor from said salt mixing tank to said secondary black liquor heater and finally to said furnace. In the present system a primary black liquor heater is housed within a salt cake mixing tank and is further provided with a secondary black liquor heater located between the heavy black liquor pump and the furnace. In the modified wet EP ash return system, the EP ash from EP rotary feeder's outlet is transported by pair of conveyors to the common chemical ash tank. In chemical ash tank the EP ash is thoroughly mixed with the incoming heavy black liquor from MEE. The salt cake is added to the system in the common chemical ash tank. The economizer bottom ash also is fed through the common conveyor to the chemical ash tank. Both the ash and the salt cake are mixed with black liquor in the same tank. Then the black liquor is pumped by chemical ash pumps to the furnace. Primary black liquor heater is provided in the common chemical ash tank. The secondary black liquor heater is provided in the black liquor line as usual. The present invention of recovering spent chemical from black liquor during the process of making paper is described hereinbelow with reference to the drawings accompanying the Provisional Specification wherein: Fig.l shows the block diagram of the existing process . Fig.2 shows the modified wet ash return system. Fig.l ofthe With reference to the. accompanying drawings, EP ash is transferred to EP ash tank (10) where heavy black liquor from multiple effect evaporator is transported and the level of black liquor in the tank is maintained with the help of ash tank level control valve. EP ash mixed black liquor from the EP ash tank is then pumped into a flow box (12) by means of EP ash pumps (11) which is ultimately transported to salt cake mixing tank (16) provided with a primary black liquor heater. In the salt cake mixing tank, salt cake (Na2SO^) is added alongwith economizer bottom ash. After thorough mixing the heavy black liquor ash is pumped by heavy black liquor pumps to the furnace through secondary black liquor heater. With reference to Fig.2, heavy black liquor from multiple effect evaporator is directly fed into chemical ash tank (26) where EP ash, salt cake and economizer bottom ash are added. The ash tank level is controlled with a control valve and the liquor is heated with a primary black liquor heater. After the heating operation, the liquor is pumped with the help of chemical ash pumps (27) into secondary black liquor heater (29) where the flow of heavy black liquor is controlled with the help of a control valve before transferring it to the furnace (30). It would be apparent from the above-mentioned description and the accompanying drawings that the present invention is much more economical for it has dispensed with the use of EP ash tank, EP ash pumps, flow box and also EP ash tank level control valve. Lesser number of equipments in the black liquor system reduces auxiliary power consumption and maintenance of the equipments. In the present invention, the lay out is much more simpler than the existing system and it requires much lesser space. Furthermore, the new system has made it very easy for the recovery of spent chemical for black liquor as compared to the existing system and the process. It may be appreciated that the above method of recovery spent chemical for black liquor during the process of making paper and the system as illustrated in the drawings is by way of an example and it does not restrict the scope of the present invention. It may further be noted that any workshop improvement or modification is possible in obtaining the same result and such modification is intended to be included within the scope of the present specification. WE CLAIM: 1. A process for recovering spent chemicals from black liquor during paper making process comprising the steps of - a) feeding electrostatic precipitator ash (9) from electrical precipitator rotary feeder to a common chemical ash tank (26); b) thoroughly mixing electrostatic precipitator ash in said common chemical ash tank with incoming heavy black liquor (7) originated in multip le effect ev apo rato r; c) adding salt cake (14) in said common chemical ash tank (26) and agitating, d) feeding into said common chemical ash tank, economizer bottom ash; (15); e) mixing thoroughly said electrostatic precipitator ash (EP ash)and salt cake (14) with black liquor in said common chemical ash tank; f) pumping (27) mixed black liquor from said common chemical ash tank to a secondary black liquor heater (29) and finally g) allowing the black liquor to pass to a furnace (30) for recovery of the spent chemicals from the black liquor. 2. A process as claimed in claim 1 wherein electrostatic precipitator ash is transported through a rotary feeder to said common chemical ash tank by a pair of conveyors. 3. A process for recovering spent chemicals from black liquor during paper making process substantially as herein described, 4 An Integrated Plant for carrying out the process as claimed in any of the preceding claims comprising an electrostatic precipitator ash tank (9), a common chemical tank (26), a secondary black liquor heater (29) and a furnace (30), said electrostatic precipitator ash tank (8) being connected to salt cake mixing tank (common chemical tank) through an electrostatic precipitator ash pump (27) and mixing salt cake (14) with black liqudr into said common chemical ash tank, a high powered pump (27) being adapted and located to connect said salt cake mixing tank with said secondary black liquor heater (29) for maintaining regular flow of black liquor from said salt mixing lank to said secondary black liquor heater and finally to said furnace. 5. An Integrated Plant as claimed in claim 4 wherein said salt mixing tank is nrovided with an in-built black liauor heater. 6. An Integrated Plant as claimed in claim 4 or 5 wherein said unit in equipped with a primary black liquor heater housed within salt cake mixing tank and a second black liquor heater located between heavy black liquor pump and the furnace. 7. An Integrated Plant substantially as herein described with reference to the drawings accompanying the Provisional Specification.

Full Text

This invention relates to a process of recovering spent chein teals from bla€ liquor during paper making process.
During the process of making paper in pulp mill, recovery boiler provides a means of recovering spent chemical from black liquor that results from the digesting process and is utilized as a steam generator by burning out the organic matters presents i» black liquor.
The heavy black liquor leaving the Multiple Effect Evaporator (MEE) in a pulp mil! is pumped to the black liquor storage tank of the chemical recovery unit (CRU) From the black liquor storage tank, heavy black liquor is transferred to EP ash tank, where it is mixed with chemical ash obtained from electrostatic Prectpitators (EP). The liquor is then pumped from EP ash tank by EP ash pumps to Salt Cake Mixing Tank (SCMT). In SCMT the make-up chemical viz Na2S04 (salt cake) is added.
From SCMT, black liquor is passed through black liquor heaters and is pumped to the black liquor spray guns through which it is finaly introduced into the furnace where it is burned. During the burning process, the ash in black liquor is liberated and reduced and, in molten state, drained from the furnace bottom through smelt spouts to Main Dissolving Tank (MDT). Since the molten ash is water soluble it is conveniently quenched and dissolved in MDT. The dissolved smelt in water is then pumped to a causticizer for further processing and recycling.
In dry Electrostatic Precipitator (EP) ash return system, the EP ash from EP rotary feeders outlet is transferred to the salt cake mixing tank by one set of conveyors. Each economizer bank is having a chain conveyor, which runs across the width of the economizer bank and collects the ash settling at the economizer bottom. This ash is fed through a rotary feeder to the common EP ash conveyor which transports both the economizer bottom ash and the EP ash to the SCMT.
In SCMT the salt cake is added to the black liquor to compensate the chemical losses in the paper making process. The incoming black liquor from MEE is thoroughly mixed with the salt cake and the ash in SCMT by agitators. SCMT is provided with black liquor heaters to maintain the black liquor temperature required for Heavy Black Liquor (HBL) pumps.
The black liquor from SCMT is pumped by HBL pumps to the furnace. A secondary black liuor heater is provided in black liquor line to maintain the black liquor temperature for firing.
In wet EP ash return system, the EP ash from EP rotary feeders outlet is transported by a pair of conveyors to the EP ash tanks. The EP ash is thoroughly mixed in EP ash tank with the incoming black liquor from MEE. Then the black liquor is pumped by EP ash pumps to SCMT through the flowbox.
Each economizer bank is having a bottom chain conveyor, which runs across the width of the economizer bank and collects the ash settling at the economizer bottom. This ash is fed through a rotary feeder to the common economizer bottom ash conveyor to the SCMT.

In SCMT the salt cake is added to the black liquor. The incoming black liquor from EP ash tank is thoroughly mixed with the salt cake in SCMT by agitators. SCMT is provided with a black liquor heater to maintain the black liquor temperature required for HBL pumps.
The black liquor from SCMT is pumped by HBL pumps to the furnace. A secondary black liquor heater is provided in black liquor line to maintain the black liquor temperature for firing.
One of the objects of the present invention is to dispense with some of the essential units of the conventional system for recovery of spent chemicals from black liquor.
Another object of the present invention is to use only a common chemical ash tank for mixing of ash from EP and economizer and make up salt-cake instead of separate EP ash tanks and salt cake mixing tanks. This eliminates a set of tanks, associated pumps and flow box.
A still further object of the present invention is to accommodate the improved system with a much lesser floow space.

A further object of this invention is to economize
the whole system and the process, by providing lesser means
and fewer steps in recovering, in the pulp mill, the spent
chemical from black liquor.
The other objects of the present invention can be clearly understood from the following paragraphs of the present specification.
According to this invention there is provided a process for recovering spent chemicals from black liquor during paper making process comprising the steps of -
a) feeding electrostatic precipitator ash from electrical
precipitator rotary feeder to a common chemical ash tank;
b) thoroughly mixing electrostatic precipitator ash
in said common chemical ash tank with incoming heavy black
liquor originated in multiple effect evaporator;
c) adding salt cake in said common chemical ash tank
and agitating;
d) feeding into said common chemical ash tank, economizer
bottom ash;

e) mixing thoroughly said electrostatic precipitator
ash and salt cake with black liquor in said common chemical
ash tank;
f) pumping mixed black liquor from said common chemical
ash tank to a secondary black liquor heater, and finally
g) allowing the black liquor to pass to a furnace for
recovery of the spent chemicals from the black liquor.
In the above process of recovering spent chemicals from black liquor the electrostatic precipitator ash is transported through a rotary feeder to the common chemical ash tank by a pair of conveyors.
The present system for carrying out a process for recovering spent chemicals from black liquor system which comprises an electrostatic precipitator ash tank, a salt cake mixing tank, a secondary black liquor heater and a furnace, said electrostatic precipitator ash tank being connected to salt cake mixing tank through an electrostatic precipitator ash pump and a flow box for transporting electrostatic precipitator ash and mixing it with black liquor

into said flow box, a high powered pump being adapted and located to connect said salt cake mixing tank with said secondary black liquor heater for maintaining regular flow of black liquor from said salt mixing tank to said secondary black liquor heater and finally to said furnace.
In the present system a primary black liquor heater is housed within a salt cake mixing tank and is further provided with a secondary black liquor heater located between the heavy black liquor pump and the furnace.
In the modified wet EP ash return system, the EP ash from EP rotary feeder's outlet is transported by pair of conveyors to the common chemical ash tank. In chemical ash tank the EP ash is thoroughly mixed with the incoming heavy black liquor from MEE. The salt cake is added to the system in the common chemical ash tank. The economizer bottom ash also is fed through the common conveyor to the chemical ash tank. Both the ash and the salt cake are mixed with black liquor in the same tank. Then the black liquor is pumped by chemical ash pumps to the furnace. Primary black liquor heater is provided in the common chemical ash tank. The secondary black liquor heater is provided in the black liquor line as usual.

The present invention of recovering spent chemical from black liquor during the process of making paper is described hereinbelow with reference to the drawings accompanying the Provisional Specification wherein:
Fig.l shows the block diagram of the existing process .
Fig.2 shows the modified wet ash return system.
Fig.l ofthe With reference to the. accompanying drawings, EP ash
is transferred to EP ash tank (10) where heavy black liquor from multiple effect evaporator is transported and the level of black liquor in the tank is maintained with the help of ash tank level control valve. EP ash mixed black liquor from the EP ash tank is then pumped into a flow box (12) by means of EP ash pumps (11) which is ultimately transported to salt cake mixing tank (16) provided with a primary black liquor heater. In the salt cake mixing tank, salt cake (Na2SO^) is added alongwith economizer bottom ash. After thorough mixing the heavy black liquor ash is pumped by heavy black liquor pumps to the furnace through secondary black liquor heater.

With reference to Fig.2, heavy black liquor from multiple effect evaporator is directly fed into chemical ash tank (26) where EP ash, salt cake and economizer bottom ash are added. The ash tank level is controlled with a control valve and the liquor is heated with a primary black liquor heater. After the heating operation, the liquor is pumped with the help of chemical ash pumps (27) into secondary black liquor heater (29) where the flow of heavy black liquor is controlled with the help of a control valve before transferring it to the furnace (30).
It would be apparent from the above-mentioned description and the accompanying drawings that the present invention is much more economical for it has dispensed with the use of EP ash tank, EP ash pumps, flow box and also EP ash tank level control valve. Lesser number of equipments in the black liquor system reduces auxiliary power consumption and maintenance of the equipments.
In the present invention, the lay out is much more simpler than the existing system and it requires much lesser space. Furthermore, the new system has made it very easy for the recovery of spent chemical for black liquor as compared to the existing system and the process.

It may be appreciated that the above method of recovery spent chemical for black liquor during the process of making paper and the system as illustrated in the drawings is by way of an example and it does not restrict the scope of the present invention. It may further be noted that any workshop improvement or modification is possible in obtaining the same result and such modification is intended to be included within the scope of the present specification.

WE CLAIM:
1. A process for recovering spent chemicals from black liquor during paper making process comprising the steps of -
a) feeding electrostatic precipitator ash (9) from electrical precipitator
rotary feeder to a common chemical ash tank (26);
b) thoroughly mixing electrostatic precipitator ash in said common
chemical ash tank with incoming heavy black liquor (7) originated in
multip le effect ev apo rato r;
c) adding salt cake (14) in said common chemical ash tank (26) and
agitating,
d) feeding into said common chemical ash tank, economizer bottom ash;
(15);
e) mixing thoroughly said electrostatic precipitator ash (EP ash)and salt
cake (14) with black liquor in said common chemical ash tank;
f) pumping (27) mixed black liquor from said common chemical ash
tank to a secondary black liquor heater (29) and finally
g) allowing the black liquor to pass to a furnace (30) for recovery of the
spent chemicals from the black liquor.

2. A process as claimed in claim 1 wherein electrostatic precipitator ash
is transported through a rotary feeder to said common chemical ash
tank by a pair of conveyors.
3. A process for recovering spent chemicals from black liquor during
paper making process substantially as herein described,
4 An Integrated Plant for carrying out the process as claimed in any of the preceding claims comprising an electrostatic precipitator ash tank (9), a common chemical tank (26), a secondary black liquor heater (29) and a furnace (30), said electrostatic precipitator ash tank (8) being connected to salt cake mixing tank (common chemical tank) through an electrostatic precipitator ash pump (27) and mixing salt cake (14) with black liqudr into said common chemical ash tank, a high powered pump (27) being adapted and located to connect said salt cake mixing tank with said secondary black liquor heater (29) for maintaining regular flow of black liquor from said salt mixing lank to said secondary black liquor heater and finally to said furnace.
5. An Integrated Plant as claimed in claim 4 wherein said salt mixing tank is nrovided with an in-built black liauor heater.
6. An Integrated Plant as claimed in claim 4 or 5 wherein said unit in
equipped with a primary black liquor heater housed within salt cake
mixing tank and a second black liquor heater located between heavy
black liquor pump and the furnace.
7. An Integrated Plant substantially as herein described with reference to
the drawings accompanying the Provisional Specification.

Documents:

835-del-2000-abstract.pdf

835-del-2000-claims.pdf

835-del-2000-correspondence-others.pdf

835-del-2000-correspondence-po.pdf

835-del-2000-description (complete).pdf

835-del-2000-drawings.pdf

835-del-2000-form-1.pdf

835-del-2000-form-19.pdf

835-del-2000-form-2.pdf

835-del-2000-form-3.pdf

835-del-2000-form-4.pdf

835-del-2000-form-5.pdf

835-del-2000-gpa.pdf

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Patent Number

216826

Indian Patent Application Number

835/DEL/2000

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

19-Mar-2008

Date of Filing

14-Sep-2000

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

BHEL HOUSE, SIRI FORT, NEW DELHI - 110 049, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	SESHADRI POYYAMMANI SETHURAMAN	SENIOR PRODUCT ENGINEER, BBP/ETS (FB) BHEL,TRICHY
2	PRAKASIYA MAXY	SENIOR PRODUCT ENGINEER, BBP/ETS (FB) BHEL,TRICHY

PCT International Classification Number

F23N 5/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA