# US 5,707,490 A · Method of recovering energy from waste liquors from pulp processes

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- Number: US 5,707,490 A
- Document ID: US5707490A
- Status: Granted
- Kind: A
- Application number: 08/634,268
- Filed: 1996-04-18
- Granted: 1998-01-13
- Earliest claimed: 1994-05-12
- Assignees: Ahlstrom Machinery Inc.
- Inventors: Marjo Kuusio; Samuli Nikkanen
- Web page: https://patentgrep.com/patent/US5707490A

## CPC

- D21C 11/06: Treatment of pulp gases; Recovery of the heat content of the gases; {Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds}
- D21C 11/125: {Decomposition of the pulp liquors in reducing atmosphere or in the absence of oxidants, i.e. gasification or pyrolysis}
- F01K 23/067: {the combustion heat coming from a gasification or pyrolysis process, e.g. coal gasification (gas turbines with fuel gasifiers F02C3/28)}
- Y02E 20/18: Integrated gasification combined cycle [IGCC], e.g. combined with carbon capture and storage [CCS]
- Y02P 70/10: Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
- D21C: PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- F01K: STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES (gas-turbine or jet-propulsion plants F02; nuclear power plants, engine arrangements therein G21D)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method of recovering energy from waste liquors from cellulose pulp processes produces high quality superheated steam, a savings in material costs is achieved, and the utilization factor of the pulp mill is improved (that is the number of shutdowns for service is reduced). A main stream of waste liquor from cellulose pulp processing is divided into first and second streams. The first stream is combusted in the recovery boiler to produce steam and the steam is fed to a superheating boiler. The second stream of waste liquor is gasified outside the recovery boiler to produce a combustible gas and an inorganic fraction. The inorganic fraction is not fed to the recovery boiler, but is separately recovered. The combustible gas is burned in the superheating boiler to superheat steam produced from combusting the first stream of waste liquor, the combustible gas providing substantially the only source of fuel for superheating the steam in the superheating boiler.

## Claims

### Claim 1

A method of recovering energy from waste liquors from cellulose pulp processes, utilizing a recovery boiler and a superheating boiler, and comprising the steps of:
(a) dividing a main stream of waste liquor from cellulose pulp processing into first and second streams;
(b) combusting the first stream of waste liquor in the recovery boiler to produce steam, and feeding the steam so produced to the superheating boiler;
(c) gasifying the second stream of waste liquor outside the recovery boiler to produce a combustible gas and an inorganic fraction, the inorganic fraction not fed to the recovery boiler; and
(d) burning the combustible gas from step (c) in the superheating boiler to superheat the steam from step (b), the combustible gas from step providing substantially the only source of fuel for superheating the steam in the superheating boiler.

### Claim 2 (depends on 1)

A method as recited in claim 1 wherein step (a) is practiced to divide the main waste liquor stream to provide about 10-35% thereof in the second stream.

### Claim 3 (depends on 2)

A method as recited in claim 2 comprising the further step of acting on at least the liquor that will be provided in the second stream so that it has a dry solids content of greater than 65% prior to the practice of step (c).

### Claim 4 (depends on 3)

A method as recited in claim 3 wherein said acting upon step is practiced by pressure heating the main waste liquor stream to a temperature higher than cooking temperature in the cellulose pulp processing to split macromolecular lignin fractions prior to the practice of step (a).

### Claim 5 (depends on 2)

A method as recited in claim 2 comprising the further step of acting on at least the liquor that will be provided in the second stream so that it has a dry solids content of between about 75-85% prior to the practice of step (c).

### Claim 6 (depends on 5)

A method as recited in claim 5 wherein said acting upon step is practiced by pressure heating the main waste liquor stream to a temperature higher than cooking temperature in the cellulose pulp processing to split macromolecular lignin fractions prior to the practice of step (a).

### Claim 7 (depends on 1)

A method as recited in claim 1 comprising the further step of purifying the combustion gas between steps (c) and (d).

### Claim 8 (depends on 1)

A method as recited in claim 1 wherein step (b) is practiced to produce steam at a temperature of less than 350.degree. C.

### Claim 9 (depends on 1)

A method as recited in claim 1 wherein step (c)is practiced under pressure, and wherein the superheating boiler is held under pressure.

### Claim 10 (depends on 1)

A method as recited in claim 1 wherein flue gases are produced in the practice of steps (b) and (d), and comprising the further step of combining the flue gases resulting from the practice of steps (b) and (d).

### Claim 11 (depends on 1)

A method as recited in claim 1 wherein step (b) is practiced in part by supplying air to the recovery boiler; and comprising the further step of utilizing flue gases produced during the practice of step (d) to preheat the air which is supplied to the recovery boiler.

### Claim 12 (depends on 1)

A method as recited in claim 1 wherein during the practice of step (d) flue gases are produced; and comprising the further step of feeding the flue gases from step (d) to a lower part of the recovery boiler.

### Claim 13 (depends on 1)

A method as recited in claim 1 comprising the further steps of, between steps (c) and (d), dividing the combustible gas from step (c) into two streams, feeding one of the streams to the superheating boiler to practice step (d), and feeding the other stream for combustion in at least one of a lime mud reburning kiln and an auxiliary boiler.

### Claim 14 (depends on 1)

A method as recited in claim 1 comprising the further step of acting on at least the liquor that will be provided in the second stream so that it has a dry solids content of greater than 65% prior to the practice of step (c).

### Claim 15 (depends on 1)

A method as recited in claim 1 comprising the further step of acting on at least the liquor that will be provided in the second stream so that it has a dry solids content of between about 75-85% prior to the practice of step (c).

### Claim 16 (depends on 15)

A method as recited in claim 15 wherein said acting upon step is practiced by pressure heating the main waste liquor stream to a temperature higher than cooking temperature in the cellulose pulp processing to split macromolecular lignin fractions prior to the practice of step (a).

### Claim 17 (depends on 1)

A method as recited in claim 1 wherein said acting upon step is practiced by pressure heating the main waste liquor stream to a temperature higher than cooking temperature in the cellulose pulp processing to split macromolecular lignin fractions prior to the practice of step (a).

### Claim 18 (depends on 1)

A method as recited in claim 1 comprising the further step of, prior to step (a), pressure heating the main waste liquor stream to a temperature of at least 170.degree. to split macromolecular lignin fractions.