IE940281A1

IE940281A1 - A pulp and sugar process

Info

Publication number: IE940281A1
Application number: IE940281A
Authority: IE
Inventors: Gerard Norton
Original assignee: Irish Sugar Research And Dev L
Priority date: 1994-03-30
Filing date: 1994-03-30
Publication date: 1995-10-04
Also published as: GB2287952A; GB2287952B; IE73273B1; GB9407765D0

Abstract

Pulp and sugar are prepared from sugar beet by a method which includes separating a major proportion of the beet molasses into residual molasses 14 and a sugar fraction 15 which is delivered into a refining process 10 for producing white sugar. All of the residual molasses 14 from the separation process 13, pressed pulp 7 and trash 3 from the beet preparation process 1 are mixed to form a pulp mixture 20. The pulp mixture is dried in dryers 30, 31. Exhaust gases 40b, 41b, 42b from separate coal fired boilers 40, 41, 42 are delivered into main supply ducts 45, 56 and a secondary duct 47. The main portion of the exhaust gases is delivered to gas mixing chambers 55,56 for the dryers. The heat content of the exhaust gases is used to achieve optimum drying conditions at maximum throughput.

Description

TRUE COPY LODGES application No...9..4..Qg~yy A Pulp and Sugar Process The invention relates to a process for preparing pulp and sugar from sugar beet.

According to the invention there is provided a process for preparing pulp and sugar from sugar beet comprising the steps of:preparing beet for processing; slicing the prepared beet; extracting sucrose by diffusion from the sliced beet to produce raw juice and pulp; pressing the pulp to remove excess water and to provide pressed pulp; purifying the raw juice; evaporating water from the purified juice to form thick juice; refining the thick juice to form white sugar and beet molasses; separating beet molasses into a sugar fraction for sugar extraction and residual molasses; mixing pressed pulp and all residual molasses generated from separation of the beet molasses to form a pulp mixture; drawing a furnace gas tempering portion of the exhaust temper the furnace gases as required prior to delivery to a gas mixing chamber; feeding the balance of the exhaust gases from the boiler to the gas mixing chamber; mixing the gases in the mixing chamber to provide a drying gas supply to the pulp dryer at less than 750°C; and drawing the mixed gas through the pulp dryer to dry the pulp.

In a particularly preferred embodiment of the invention, the furnace gas tempering portion of the exhaust gases from the boiler are drawn directly to the furnace of a pulp dryer without passing through an economiser.

In a preferred arrangement there are at least two boilers and furnace gas tempering portions of the exhaust gases from each boiler are drawn directly to the furnace of a pulp dryer.

In a particularly preferred arrangement there are two pulp dryers arranged in parallel and the pulp mixture is divided between the dryers.

Most preferably the pulp mixture in one of the pulp dryers is dried by the boiler exhaust gases only.

In a particularly preferred arrangement the or each boiler is a coal fired boiler.

In one embodiment of the invention the beet is prepared for processing by a method which includes removing beet leaves from the beet to form beet trash and the method includes the step of mixing the trash with the pulp mixture.

In one embodiment of the invention the beet trash is macerated and then mixed with water to form a slurry for pumping to a pulp mixer.

Preferably the slurry is passed over a screen to separate the water from the slurry prior to addition to the pulp mixer. In a preferred arrangement the screened trash is passed through a centrifuge to remove further water prior to addition to the pulp mixer.

In one arrangement the method includes the step of pelletising the dried pulp.

The invention also provides pulp and sugar whenever produced by a process of the invention.

The invention will be more clearly understood from the following description thereof, given by way of example only with reference to the accompanying drawing which is a diagrammatic view of a process for preparing pulp and sugar from sugar beet by the process of the invention.

Referring to the drawing there is illustrated a process for preparing pulp and sugar from sugar beet according to the invention which comprises in step 1 preparing beet for processing by removing clay, stones, beet leaves, weeds and the like. The beet leaves are separated and collected in the form of trash. The trash is macerated and then mixed with water form a slurry, the slurry is pumped along line 2 to a screen for water separation and then passed through a centrifuge to remove further water. In step 3 the prepared beet is sliced and a sugar solution which is referred to as raw juice is extracted by a diffusion process in step 4 which also produces pulp which is delivered along a line 5 to a pulp press 6 which produces pressed pulp 7.

The raw juice is purified in step 8 in a number of operations including liming, saturation, filtration, deliming and sulphitation which produces a purified sugar solution known as thin juice. The thin juice is evaporated in step 9 in a number of stages to produce a more concentrated sugar solution which is referred to as thick juice. The thick juice from the evaporation process is refined in step 10 by a number of processes including filtration, crystallisation, centrifugation, further crystallisation and further centrifugation.

The products from the refining process are white sugar 11 and beet molasses 12. The major proportion of the beet molasses 12 is separated in step 13, for example by means of an ion exclusion process, into residual molasses 14 and a sugar fraction 15 which is delivered into the refining process 10 for producing white sugar 11. The beet molasses 12 may also be delivered directly to storage 16 from which it may be delivered directly to a mixing step 19 in which all of the residual molasses 14 from the separation process 13, the pressed pulp 7 and the trash 2 from the beet preparation process 1 are mixed together to form a pulp mixture 20.

The pulp mixture 20 is delivered to one of two rotary pulp dryers 30, 31 in which the pulp mixture is dried to produce dried pulp 32 which may be shredded or pelletised for animal feed.

Power is supplied for running the various machines used in the process of the invention by three separate coal fired boilers 40, 41, 42 to which coal is delivered along supply lines 40a, 41a, 42a from a common supply 43. Steam generated by the boilers is used to drive an electricity generating plant. The exhaust gases 40b, 41b, 42b which are typically at 400°C is delivered into main supply ducts 45, 46 and to a secondary duct 47 from which a furnace gas tempering portion of the exhaust gases is drawn by fans 48, 49, 50 to furnaces 51, 52 for the rotary pulp dryers , 31, respectively.

The main portion of the exhaust gases from the boilers 40, 41, 42 is delivered along the ducts 45, 46 to gas mixing chambers 55, 56 respectively of the rotary pulp dryers 30, 31. In the chambers 55, 56 hot gases generated in the furnaces 51, 52 are mixed with exhaust gases from the boilers to provide drying gas for the dryers 30, 31 at optimum temperatures to achieve optimum drying conditions for the pulp mixture 20. Typically the burner gases are at a temperature of from 1600 to 1800°C, the exhaust gases from the boilers are at about 380°C and the mixing produces drying gases at a temperature of approximately 700°C for drying the pulp mixture 20.

It will be noted that the exhaust gases from the boilers do not pass through economisers. Their heat content is used optimally for providing drying gases for the pulp dryers to achieve drying conditions for the pulp mixture at maximum throughput with consequent maximum production of pulp mixture.

The fans 48, 49, 50 are arranged and various dampers are provided in the exhaust gas ducts to optimise the use of the furnace gas tempering portion of the boiler exhaust gases.

It has been found that by using the exhaust boiler gases directly to temper the furnace gases in the furnaces and for mixing with the furnace gases prior to delivery to the dryer the operation not only of the boilers but also of the furnaces is optimised. This allows the furnaces and boilers to be operated at maximum efficiency with consequent optimisation of energy resources. In addition, the configuration allows maximum throughput of pulp mixture to be efficiently dried. Thus, all residual molasses 14 from the separation process 13 is utilised so that the separation process 13 can be operated at maximum throughput giving optimum sugar fraction recovery and thus optimising the refining process 10 in general to in turn optimise the production of white sugar.

The arrangement also facilitates the operation of one of the dryers 30, 31 using exhaust boiler gases only i.e. without operating the dryer furnace. This may arise in some situations where the pulp mixture volume to be processed is not sufficient to run both dryers at optimum efficiency. In this case one of the dryers 30, 31 is operated at full capacity and the other dryer is operated at reduced capacity using the boiler exhaust gases only. In this way the arrangement may be readily adjusted to mirror production demand.

The invention is not limited to the embodiments hereinbefore described, which may be varied in detail.

Claims

1. A process for preparing pulp and sugar from sugar beet comprising the steps of:preparing beet for processing; slicing the prepared beet; extracting sucrose by diffusion from the sliced beet to produce raw juice and pulp; pressing the pulp to remove excess water and to provide pressed pulp; purifying the raw juice; evaporating water from the purified juice to form thick juice; refining the thick juice to form white sugar and beet molasses; separating beet molasses into a sugar fraction for sugar extraction and residual molasses; mixing pressed pulp and all residual molasses generated from separation of the beet molasses to form a pulp mixture; drawing a furnace gas tempering portion of the exhaust gases from a boiler to a furnace of a pulp dryer to temper the furnace gases as required prior to delivery to a gas mixing chamber; feeding the balance of the exhaust gases from the boiler to the gas mixing chamber; mixing the gases in the mixing chamber to provide a drying gas supply to the pulp dryer at less than 800°C; and drawing the mixed gas through the pulp dryer to dry the pulp.

2. A process as claimed in claim 1 wherein the furnace gas tempering portion of the exhaust gases from the boiler are drawn directly to the furnace of a pulp dryer without passing through an economiser.

3. A process as claimed in claim 1 or 2 wherein there are at least two boilers and furnace gas tempering portions of the exhaust gases from each boiler are drawn directly to the furnace of a pulp dryer.

4. A process as claimed in any preceding claim wherein there are two pulp dryers arranged in parallel and the pulp mixture is divided between the dryers .

5. A process as claimed in claim 4 wherein the pulp mixture in one of the pulp dryers is dried by the boiler exhaust gases only.

6. A process as claimed in any preceding claim wherein the or each boiler is a coal fired boiler.

7. A process as claimed in any preceding claim wherein the beet is prepared for processing by a method which includes removing beet leaves from the beet to form beet trash and the method includes the step of mixing the trash with the pulp mixture. 5

8. A process as claimed in claim 7 wherein the beet trash is macerated and then mixed with water to form a slurry for pumping to a pulp mixer.

9. A process as claimed in claim 8 wherein the slurry is passed over a screen to separate the water from 10. The slurry prior to addition to the pulp mixer.

10. A process as claimed in claim 9 wherein the screened trash is passed through a centrifuge to remove further water prior to addition to the pulp mixer. 15 11. A process as including the claimed in any preceding step of pelletising the dried claim pulp. 20 13 A process for preparing pulp and sugar substantially as hereinbefore described with reference to the accompanying drawings. Pulp and sugar whenever produced by a process as claimed in any preceding claim.