A METHOD AND A SEPARATING PRESS FOR USE IN THE PRODUCTION OF BIOETHANOL

The prior art

The invention relates to a method of producing bioethanol on the basis of ground plant material, such as corn, said material being suspended in water and heated to above the gelatinization temperature, following which a heat stable α-amylase is added, said mixture being boiled to form a mixture having a high dry matter content, following which glycoamylase and yeast are added to said mixture to form ethanol by distillation, as well as a separating press for use in the performance of the method.

In the previously known methods of producing ethanol on the basis of plant material, such as corn and sugar cane, etc., this preferably takes place by a dry production, i.e. dry grinding to a particle size of about 1 mm.

This granulate is then suspended in water, which is heated to max. 90 ⁰ C to get above the gelatinization temperature of the starch content.

Then, a heat stable cr-amylase is added, which hydrolyzes the starch to reduce the viscosity thereby.

The mixture is then boiled at a temperature of max. 120 ⁰ C, whereby the starch in the liquid will be converted into oligosaccharides.

It is intended to ensure a high dry matter content in the mash to achieve the maximum capacity thereby (very high gravity technology).

The next process step is to decompose saccharides into glycose, which is converted into ethanol by addition of yeast.

Finally, this ethanol is distilled off, following which the insoluble parts of the sediment are removed.

This takes place in either a decanter or a centrifuge in order for the liquid in the sediment to be utilized, preferably by supply to the suspension process step.

Known separators, however, are vitiated by the drawback that they are not very effective in a continuous process, but are solely intended for a single process step, and to this should be added that they are every expensive in operation because of a great consumption of energy. Moreover, they require much maintenance and cleaning, and, finally, the dry matter content, or in other words the degree of separated liquid, is not sufficient to cover the costs of operation. Therefore, the utilization rate in the production of ethanol is not optimum.

The object of the invention

It is the object of the invention to improve the production process, and this is achieved according to the invention in that the insoluble parts of the distillation residue, the sediment, are supplied to a separating press at a variable compression pressure to separate liquid from the sediment.

Hereby, the utilization rate is optimum, since the dry matter content is very high, and as much liquid as possible is utilized in the production process to form ethanol.

It has surprisingly been found that the pulsation established during the pressing, gives an unprecedentedly high expulsion of liquid, which is re- lated to the effect which is achieved when a hard compression is followed by a less hard compression, whereby the liquid is pulled out of the mass, is

released and can be separated and discharged.

When, as stated in claim 2, a separating press comprising a conveyor and compression worm, which extends inside a screen shell with small screen holes, is used, and a valve at the discharge end exerts a variable counter- pressure, it is ensured that a continuous process may be carried out.

When, as stated in claim 3, the valve body is configured such that it performs a cycle of movement which alternately opens and restricts the dis- charge opening, it is possible to control the process by scanning the absorption of energy of the drive motors and thereby ensure specific valve positions to achieve the desired pressure conditions.

When, as stated in claim 4, the valve seats are configured such that the flow courses are uniform in the various valve positions, an even flow through the press is achieved.

Finally, as stated in claim 5, it is expedient to provide the valve body with a sealing ring, since a completely closed valve position may be achieved hereby.

The drawing

An example of a separating press according to the invention will be de- scribed more fully below with reference to the drawing, which shows a partially sectional view of a press and an enlarged view of the valve part.

Description of the exemplary embodiment

A separating press, which is suitable for performing the method of producing ethanol by expulsion of liquid from the sediment after the actual distilla-

tion for the separation of the ethanol has been performed, will be described more fully below.

The press itself is formed by one or more cylindrical screen shells 2a-2c, which are joined adjacently to form a cylinder by means of flanges 3.

The screen shells may have different screen openings, e.g. openings of 0.2 mm in the first shell 2a and openings of 30 μm in the last shell 2c.

Supply of the sediment 9 takes place to the interior of the screen shell, in which a worm 5 on a shaft 4 rotates. The sediment 9 is hereby fed into the press chamber 11 , which extends between the screen shells 2a-2c and the shaft 4 and the worm turn 5 to advance the sediment toward the discharge opening 14 at the opposite end of the press.

A valve is mounted at the discharge end of the press chamber 11 , said valve being shown more clearly in the enlarged view.

The valve body 17 itself is provided with a seat 18 which is bevelled in one or more angles to form an obliquely extending discharge.

The valve body 17 cooperates with a valve seat 15 on the rear edge of the screen shell 2c, said seat 15 being likewise bevelled corresponding to the cooperating seat 18.

A sealing ring 16 is shown on the valve seat 18, which sealing ring will block the discharge from the press chamber 11 at a closed valve position.

The valve body 17 may be adjusted by means of working cylinders (not shown) so that it may be displaced in the direction of the double arrow, i.e. for engagement and opening.

The screen shells 2a-2c are rotated with a few revolutions per minute in one direction by means of a motor 6 via a gear 8, and the worm 4, 5 rotates in the opposite direction by means of another motor 7 and gear 8, likewise with a few revolutions per minute.

Finally, a collection chute 12 is provided for the collection of liquid, and a discharge is provided for the discharge of liquid 13 during the pressing.

The method of expelling liquid from the sediment will now be explained.

The sediment with a shown liquid content, after the ethanol has been distilled off, is fed via an inner channel 10 to the press chamber 11 , as indicated by an arrow 9.

At the beginning, the valve 17 is closed against discharge so that the turns on the worm 5 will advance the sediment to the right in the drawing when the worm is started.

During this feeding, the sediment is compressed, as air and liquid are ex- pelled through the screen openings.

When a suitable period of time has elapsed, a pressure has been generated, and the sediment will engage the valve 17, following which the pulsation of the valve body is initiated, viz. by a movement in a forward and rearward direction.

This pulsation contributes to expelling the liquid, which is collected at the bottom and is discharged, following which the liquid may be returned to the soaking step of the process.

It is this pulsation and switching between a higher and a lower pressure

which contributes to an unprecedentedly high efficiency, which takes place during the continuous feeding of sediment and expulsion of liquid. When the pressure drops, the liquid in the sediment tends to flow from the compressed sediment to be pressed out of the sediment as liquid in the subse- quent compression.

The valve movement may be controlled by the absorption of energy of the motors 6,7, as the absorption of energy of the motors and the degree of compression will be related.