JPS5834116B2 - starch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering waste heat from a process in which starch sugar is produced mainly by an enzymatic decomposition method.

Generally, in the starch saccharification industry, acid decomposition and enzymatic decomposition are methods for decomposing starch to produce sweet substances.

In particular, when producing glucose as a sweet substance, the enzymatic decomposition method is currently used because it yields glucose with higher purity than the acid decomposition method.

The process of hydrolyzing starch by this enzyme mainly consists of two steps: liquefaction and saccharification. Liquefaction roughly cuts starch molecules into water-soluble dextrin, and saccharification breaks down this dextrin to produce glucose. The liquefaction and saccharification processes use enzymes suitable for each process.

The liquefaction process is not simply a pretreatment for the saccharification process; the suitability of liquefaction is an important process that not only has a negative impact on the purification process and subsequent cleaning processes such as decolorization, but also influences the purity of the product.

Conventionally, this liquefaction process was performed at an operating temperature of 8°C in order to deactivate the enzyme.
The temperature range is 0 to 90°C, but when using above-ground starch such as cornstarch as a raw material, the content of poorly soluble starch is higher than underground starch such as sweet potato starch, so the conventional method is carried out under the above operating conditions. In this case, cleavage of poorly soluble starch molecules remained, and satisfactory liquefaction could not be achieved.

As a method to completely liquefy this poorly soluble starch, the liquefaction process is divided into two stages, the first and third stages, and after the remaining liquefied starch molecules are swollen and decomposed under high temperature and high pressure conditions, the liquefaction process is carried out again using enzymes. The so-called two-stage liquefaction method, in which the temperature is lowered to a temperature at which the Steam consumption will be a dog.

- In the next liquefaction, starch milk is heated to a high temperature and a catalyst such as a liquefaction enzyme or acid is added to hydrolyze it and convert it into glucose.
, about 130°C) and also contains coagulable starch proteins such as dextrin, which tends to cause scaling, so generally the pressure is returned to normal using a flash cooler and the liquid temperature is lowered to about 90°C.

The steam generated at this time is condensed in a barometric condenser, but the waste heat at that time is released to the outside together with waste water.In other words, the cooling water of this barometric condenser is recovered as low-temperature water and used as hot water in the manufacturing process. Even if the cooling water is used, the amount of cooling water is large compared to the amount of hot water required, so most of it is discarded as waste water or dissipated in the cooling water saw, resulting in about 30% being wasted, reducing thermal efficiency. Unfortunately, not only was waste heat hardly utilized, but it also caused pollution problems such as heated waste water, the manufacturing cost was relatively high, the equipment cost was high and it was uneconomical, and live steam was used for heating during the cleaning process. There was a risk that the product would overheat and cause defects such as discoloration.

Furthermore, barometric condensers are conventionally used as a method to condense the steam generated in the liquefaction process, but since this is a method of condensing by bringing cooling water and steam into direct gas-liquid contact, it can be used instead of cooling water. When using sugar solution,
This method is not suitable as a heating method in the cleaning process because the condensed water may dilute and contaminate the sugar solution.

The present invention eliminates the above-mentioned drawbacks of the conventional one by considering the entire starch sugar production process and recovering an appropriate amount of the heat obtained in the cooling process related to the liquefaction process in the heating process related to the subsequent cleaning process. The purpose of the present invention is to provide an effective method for recovering waste heat in a starch sugar production process using an enzymatic decomposition method that can effectively recover waste heat, have high thermal efficiency, and prevent overheating of the product. It is something.

The present invention detects the liquid temperature at the exit temperature of the heating medium after heating in order to selectively guide the vapor generated in the first primary liquefaction step in the multi-stage cooling step related to the liquefaction step to the surface condenser in the heating step related to the cleaning step. This method of recovering waste heat from a starch sugar production process is characterized in that the heating capacity applied to the liquid in the surface condenser is changed by operating a valve in the liquid line.

To explain the present invention with reference to an example, in the enzymatic saccharification process as shown in FIG.
After processing at a high temperature and high pressure of approximately 100°C, the liquid temperature is cooled to 80 to 90°C for secondary liquefaction, and this cooling method is generally carried out in a flash cooler 1 connected to a vacuum source. This is carried out by a self-evaporative cooling method, and the heat generated at this time is not discarded but is led together with steam to the heating step of the cleaning step described later.

In other words, the liquid that has undergone secondary liquefaction goes through a saccharification process and is then purified as a saccharified liquid through filtration and cleaning processes to produce a product.In this cleaning process, the main method is generally a combination of activated carbon and ion exchange. The optimal temperature for these cleaning equipment is a high temperature of about 70°C for the activated carbon process, and a low temperature of about 40°C for the ion exchange process, so heating and cooling must be performed.

The liquid at about 40°C that has been subjected to ion exchange decolorization is heated to about 70°C for the next activated carbon decolorization. The waste steam is led to the surface condenser 3 and used as a heating source for the sugar solution.

Generally, the amount of heat required for this heating is 1 flash cooler.
Since the amount of heat generated is almost the same as the amount of heat generated in

The heat transfer area of the surface condenser 3 is determined to be sufficient to condense the entire amount of generated steam.

On the other hand, since the liquid has fluctuations in flow rate, temperature, etc., if the capacity of the surface condenser 3 is constant, there is a possibility that the outlet liquid temperature will fluctuate.

In order to prevent this and keep the outlet liquid temperature almost constant, the following control method is adopted as an embodiment.

In other words, since the steam generated in the liquefaction process generates a little more heat than the amount of heat required in the cleaning process, it is necessary to detect the exit temperature of the surface condenser of the sugar solution and adjust the steam to maintain it at the set value. All of the steam generated must be condensed and discharged from the system.

For this reason, the steam at the inlet of the surface condenser cannot be adjusted directly, so by installing a bypass pipe in the surface condenser and controlling the automatic valve installed there, excess steam is condensed in the barometric condenser installed afterwards.

In this system, the amount of heat required on the liquid side is generally smaller than the amount of heat supplied by the steam, so in order to control this, the temperature of the outlet liquid 4 of the surface condenser 3 is detected and installed in the bypass 5 as shown in Figure 2. A temperature regulator 7 is provided to automatically operate the valve 6. When steam becomes surplus to the liquid and the temperature of the outlet liquid 4 rises, the temperature regulator 7 automatically operates the valve 6.
The valve 6 is opened, and the excess steam passes through the bypass 5 and directly enters the barometric condenser 2 and is disposed of, thereby controlling the amount of heat given to the liquid in the surface condenser 3.

In addition, as an example of another control method, as shown in FIG. 3, the temperature of the outlet liquid 4 of the surface condenser 3 is detected and the valve 9 for opening and closing the drain circuit 8 of the surface condenser 3 is automatically operated. A temperature regulator 10 is provided, and when steam becomes surplus to the liquid and the temperature of the outlet liquid 4 rises, the valve 9 is closed by operating the temperature regulator 10, and when drain accumulates in the surface condenser 3, the heat transfer area increases. Since the amount of heat given to the liquid decreases, the amount of heat given to the liquid also decreases, and the outlet liquid 4
The temperature of the liquid decreases and the excess steam enters the IJ rack condenser 2 and is disposed of, controlling the amount of heat given to the liquid in the surface condenser 3.

Compared to the method of the first control embodiment, this method is advantageous in terms of installation and cost because the piping size is generally smaller and bypass piping is not required.

In such a process, when the plant is started, steam is generated and the liquid reaches the surface condenser 3 with a delay of several days, and when the plant is stopped, the liquid remains until several days after the steam has disappeared.

To deal with this, a bypass valve 11 as shown in FIG.
Since there is no liquid yet at startup and steam cannot be condensed by surface condenser 3, this bypass valve
1 to open the valve 1 and send the entire amount directly to the barometric condenser 2 for condensation, and also detect the temperature of the outlet liquid 4 of the surface condenser 3 and operate the valve 12 for introducing steam from another steam source. In order to compensate for the lack of steam and the lack of a heating source when the system is stopped, the temperature control 513 detects the temperature of the outlet liquid 4 and opens the valve 12 as necessary to maintain the liquid temperature at the set value without compensating for steam. is valid.

In Figures 2 and 3, a heater is not required during normal operation, but when the liquefaction process is stopped, there is a delay of about 3 days until it reaches the saccharification tank, so a heating heater is installed. It is.

The temperature controller 14 is used to detect the heater outlet temperature and operate a valve 15 from another steam source to introduce steam as necessary to control the liquid temperature.

During normal operation, if the amount of heat generated and consumed is balanced, barometric capacitor 2 is not necessary. In the case of unbalance, and especially during startup, surface capacitor 3
This is necessary in case there is no liquid in the tank.

In addition, this method is not limited to the enzymatic method, but also uses the flash cooler attached to the saccharification process under high temperature and high pressure, such as conventional continuous saccharification methods using acid decomposition (e.g. Kroyer method, Cohn product method, Onlater method). Similar heat recovery is also possible in equipment that has the same type of heat as shown in Figure 5.

Since this embodiment is configured as described above, the steam generated in the cooling process related to liquefaction is not wasted and is used to increase or decrease the amount of heat given to the liquid in the surface condenser, which is the heating process of the cleaning process. By doing so, it is possible to achieve rational heat recovery, greatly reduce operating costs compared to conventional methods, and prevent pollution caused by waste heat. Because live steam was used to heat the liquid, the sugar liquid was easily overheated, and if the sugar liquid was in contact with high temperatures for a long time, there was a risk of coloring due to overheating.Coloring would increase the load on the cleaning process and lead to product defects. It's going to happen.

For this reason, complicated instrumentation and control equipment was required to prevent the risk of overheating and discoloration, but in this method, the steam generated in the flash cooler does not rise above 90°C, and it is heated according to the required amount. Since the feed rate is controlled, there is no risk of overheating the liquid, and no instrumentation control equipment is required, which simplifies the equipment structure and handling, especially for starch sugar production.

That is, the live steam used in a glucose manufacturing factory is usually 12
It has a saturation temperature of about 0 to 160℃, and if this steam is used for the heating process in the cleaning process, it will be exposed to high temperature conditions for a long period of time if the transfer of sugar solution is stopped due to an accident. In order to prevent any inconvenience, safety devices such as instrumentation control equipment that detects the stoppage of the sugar solution and automatically stops the supply of steam are required, but with this method, the steam generated during the liquefaction process is Due to the low temperature of this recovered steam, there is no risk of these problems occurring at all, so safety equipment and associated equipment are unnecessary, and ease of use is also a major advantage.

In addition, the conventional method uses a barometric condenser, which requires a large amount of cooling water, which is disadvantageous in terms of measures against hot waste water, but by condensing steam in a surface condenser, no cooling water is required. This makes starch sugar production process advantageous**, and can be easily applied not only to enzymatic methods but also to continuous saccharification methods using acid decomposition, and the amount of steam used in saccharification and concentration equipment can be greatly reduced. You can save money.

When using this method, it has been confirmed that in some examples, the amount of steam saved reaches about 15% as shown in the table below. This has an extremely great practical effect in that it prevents product defects due to overheating when it is no longer used, and enables the production of high-quality starch sugar at low cost.

[Brief explanation of drawings]

The drawings are flowcharts showing embodiments of the present invention; FIG. 1 shows the overall flow of starch sugar production by an enzymatic method, and FIGS. 2 and 3 show a part of the flowchart together with the control mechanism, FIG. 4 shows a part of a flow diagram showing control at startup and stop, and FIG. 5 shows a flow diagram of starch sugar production by acid decomposition method. 1...Flash cooler, 2...Barometric condenser-13...Surface condenser, 4...Outlet liquid, 6...
valve,? , 10゜13.14...Temperature controller, 9,12,15...Valve, 11...
・Bypass valve.

Claims (1)

[Claims] In the starch sugar production process, which consists of the steps of primary liquefaction, secondary liquefaction, saccharification, filtration, and purification, the poorly soluble starch molecules remaining in the secondary liquefaction are swollen and decomposed under high temperature and high pressure conditions, and then re-processed. Secondary liquefaction is carried out by lowering the temperature to the temperature at which enzymes act, and the entire amount of steam generated in the self-evaporative cooling process in the flash cooler following the primary liquefaction process in which starch milk is treated under high temperature and pressure is transferred to the subsequent cleaning process. A temperature controller that detects the outlet liquid temperature of the surface condenser and outputs an operation signal by guiding the liquid to a surface condenser in the heating process and condensing the entire amount of the generated steam, and controlling the temperature of the surface condenser according to changes in the outlet liquid temperature. Automatically operates a valve provided in the introduction line or outlet line for the heat medium introduced into or taken out of the surface condenser, bypasses excess steam to the liquid, and increases or decreases the amount of heat given to the liquid in the surface condenser. 1. A method for recovering waste heat from a starch sugar manufacturing process.