JP2009024031A - Separation/concentration system for bio-gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively and easily utilize a bio-gas by performing response-control without causing a hunting phenomenon or the like such that a concentration gas concentration becomes a target concentration value even if the concentration of the bio-gas and the concentration gas concentration are varied by disturbance during operation of the separation/concentration system. <P>SOLUTION: The separation/concentration system for the bio-gas is provided with a separation/concentration means 2 for separating the concentrated methane gas from the bio-gas fed through a flow rate adjustment means 1; a control means 4 for comparing/operating the target concentration value of the methane concentration of the concentrated methane gas with the methane concentration detected by the detection means 3 and PID-controlling the flow rate adjustment means 1; and a restriction means 5 for setting an upper limit value L of a feed amount of the bio-gas by restricting variation of a PID-control amount P<SB>t</SB>by the formula: L="the feed amount of the bio-gas in the case of P<SB>t</SB>=100%"×(P<SB>t</SB>+(P<SB>0</SB>×W)) (wherein 0≤P<SB>t</SB>, P<SB>0</SB>, W≤100% and P<SB>t</SB>+(P<SB>0</SB>×W)<100%). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a separation / concentration system for biogas, which is applied to, for example, biogas generated when animal or plant waste is biodegraded, and methane gas contained in the biogas is separated and concentrated. It is related with the system for effective use.

  2. Description of the Related Art Conventionally, there are many techniques for separating and concentrating a mixed gas containing two or more gas components by a system (hereinafter referred to as a separation and concentration system) including a separation and concentration means (separation membrane stack) comprising gas separation membranes. Research and development are underway. For example, it is applied to biogas generated when animal and plant waste (waste biomass etc.) is biodegraded (decomposed by bacteria etc.), and methane gas contained in the biogas is used. Attempts have been made to separate and concentrate for effective use (utilized as alternative energy; for example, fuel for gas turbine engines) (for example, Patent Document 1 regarding separation and concentration technology).

  When the biogas is passed through the gas separation membrane, each gas component in the biogas is selectively separated, and a target concentrated gas is obtained. For the gas separation membrane, a thin film made of a polymer material (polyimide or the like) such as polyolefin, cellulose, or silicon is used according to the target concentrated gas.

  For example, when the concentration of each gas component of the biogas itself is constant, the amount of mixed gas passing through the gas separation membrane per unit time (that is, the amount of biogas supplied to the separation and concentration means (hereinafter referred to as biogas supply amount)) And the methane concentration of the concentrated methane gas (hereinafter referred to as the concentrated methane concentration) can be expressed by a characteristic line having a negative slope as shown in FIG. 4, for example. That is, the concentrated methane concentration decreases as the biogas supply amount increases (in FIG. 4, it converges at a constant concentration value).

  The separation / concentration gas obtained by the separation / concentration system is generally often used while maintaining a substantially constant concentration. The concentration may change due to a change in the concentration and the separation / concentration efficiency, and the effective use may be difficult. For this reason, it is necessary to detect the state of the system and perform control so that the concentration of the concentrated gas is always substantially constant (for example, correction control so that the target concentration value is set in advance). For example, system control factors (factors that change the separation and concentration efficiency of the separation and concentration means, etc.) are measured in advance, and response control is performed so that the concentrated gas is as set (target concentration value). Feed-forward method that responds so that the concentration reaches the target concentration value, or response control that adjusts the amount of biogas (flow rate described later) A feedback-type separation and concentration system that controls the adjusting means and adjusts the biogas supply amount)) has been studied (for example, Patent Document 2 regarding the feed-forward method).

  In the feedforward system, the configuration of the separation and concentration system becomes relatively complicated, but an instantaneous response is possible with high accuracy (for example, error is about 0.1% or less). On the other hand, in the feedback method, although the response time is relatively long, it has sufficient accuracy and the configuration of the separation and concentration system is relatively simple.

  In particular, in the case of a biogas separation and concentration system, a predetermined time is required until the concentrated methane gas is extracted from the biogas (having a large time constant), and high-precision control as in the feed-forward method is not necessary. Therefore, many feedback methods are applied. Further, as a method for improving the control accuracy of the feedback method, for example, a P operation for generating a signal proportional to the control deviation according to the difference between the target density value and the detected density value after control, or integration of the control deviation PID control for performing I operation and D operation for generating a signal proportional to the value and the differential value is applied.

  FIG. 5 is a schematic explanatory diagram showing an example of a separation and concentration system that performs PID control. In FIG. 5, first, the biogas is supplied (introduced) to the separation and concentration means 2 having a gas separation membrane while the flow rate is adjusted by a flow rate adjustment means (MFC (mass flow controller) 1 or the like). In the separation and concentration means 2, the biogas is separated into methane gas and carbon dioxide gas, and concentrated methane gas is obtained. The concentrated methane concentration of the concentrated methane gas is detected by a concentration detecting means (such as a concentration meter for the concentrated gas) 3, and the detection result (detection signal) is sent to the control means (means that can perform PID control by comparison). .

  In this control means 4, the target concentration value of the concentrated methane concentration and the biogas supply amount at the start of operation of the flow rate adjusting means 1 corresponding to the target concentration value are set. Further, after the operation of the flow rate adjusting unit 1 is started, the target concentration value is compared with the detection result, and the flow rate adjusting unit 1 is subjected to PID control (command signal is transmitted) according to the comparison result.

  For example, assuming that the concentration of each gas component of the biogas itself in FIG. 5 is constant, if the concentrated methane concentration decreases below the target concentration value, the biogas supply is based on the characteristic line as shown in FIG. The amount is suppressed. On the other hand, when the concentrated methane concentration increases above the target concentration value, the biogas supply amount increases.

  However, the concentrated methane concentration may change due to various disturbances during operation of the separation and concentration system (for example, at the start of operation), in addition to changing due to various devices of the separation and concentration system. Examples of the disturbance include a phenomenon in which the concentration of each gas component in the biogas becomes uneven or the separation and concentration conditions (temperature, etc.) change.

  For example, when the gas component concentration of the biogas itself (such as the methane concentration before concentration) further decreases due to a disturbance while the methane concentration is low and the biogas supply amount is being suppressed, There is a possibility that the biogas supply amount may be further suppressed (that is, suppressed more than necessary). Conversely, if the methane concentration is high and a disturbance in which the methane concentration is high when the biogas supply amount is increased, the biogas amount is further increased.

  In the case of PID control, the control balance is lost, and unexpected response control is triggered. And since a hunting (vibration) phenomenon is likely to occur, there is a risk that the intended control cannot be performed. Such a phenomenon becomes conspicuous in, for example, a system with a simple PID control function (for example, a system having a control unit with fixed PID control parameters and costs of several tens of thousands of yen).

It should be noted that an extremely advanced PID control function, for example, a separation / concentration system (for example, a system having a control means with a cost of about several million yen) having a function capable of constantly adjusting (increasing) the parameters of D operation in PID control is applied. Thus, a method corresponding to the hunting phenomenon is known, but such a system is expensive, and the biogas separation and concentration system has a relatively large time constant, and the effect of the parameter adjustment described above. Can hardly be obtained.
JP 2000-218126 A Japanese Patent Laid-Open No. 61-141787.

  Therefore, in the field of separation and concentration systems related to biogas, even if the concentration of the biogas and the concentration of the concentrated gas change due to disturbance during the operation of the system, even if hunting phenomenon occurs due to unexpected response control, It is desired to make the biogas easy to use effectively by eliminating the hunting phenomenon and performing response control (controlling the flow rate adjusting means to adjust the biogas supply amount) so that the concentrated gas concentration becomes the target concentration value. It was.

  The present invention solves the above-mentioned problem, and in the PID control of the separation and concentration system for biogas, the biogas supply amount is controlled in accordance with the change in the concentration of the concentrated gas, and the variation in the control amount is controlled. By limiting, even if the concentration of biogas or concentrated gas changes due to disturbance during operation of the system, response control can be performed so that the concentrated gas concentration becomes the target concentration value without causing a hunting phenomenon etc. System related.

Specifically, the invention according to claim 1 includes a separation and concentration unit that includes a gas separation membrane and separates concentrated methane gas from biogas, a flow rate adjustment unit that adjusts a biogas supply amount to the separation and concentration unit,
Detecting means for detecting the methane concentration of the concentrated methane gas obtained by the separation and concentrating means; and setting a biogas supply amount at the start of operation of the flow rate adjusting means corresponding to the target concentration value of the methane concentration; And a control means for performing PID control of the flow rate adjusting means so that the methane concentration becomes a target concentration value based on a result of the comparison and a detection result by the detection means, and a PID control amount ( hereinafter referred to as start control amount) PID control amount after the operation start referenced to P ₀ (hereinafter, referred to as after the start control amount) the variation rate of P _t and is W, equation (1) (where 0 ≦ P _t , P ₀ , W ≦ 100%, and P _t + (P ₀ × W) <100%) to limit the variation of the control amount P _t after the start, and the upper limit value L of the biogas supply amount And a limiting means for setting That is a separation and concentration system for biogas. L = “Biogas supply amount when P _t = 100%” × (P _t + (P ₀ × W)) (1).

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, each parameter of the PID control in the control means is fixed.

  The invention described in claim 3 is the invention described in claim 1 or 2, characterized in that the variation rate W is 35% or less.

  According to the first to third aspects of the present invention described above, even if the control amount after the start increases (that is, the biogas supply amount increases so as to become the maximum value), the biogas supply amount is limited by the upper limit value. .

  As described above, according to the first to third aspects of the present invention, the concentration of the biogas and the concentration of the concentrated gas change due to disturbance during the operation of the system, causing unexpected response control and causing a hunting phenomenon or the like. However, the hunting phenomenon can be eliminated, response control can be performed so that the concentration of the separated concentrated gas becomes the target concentration value, and the biogas can be effectively used.

  Hereinafter, an example of the separation and concentration system for biogas in the present embodiment will be described in detail with reference to the drawings. 4 and 5, the same reference numerals and the like are used and detailed description thereof is omitted as appropriate.

  In this embodiment, the separation concentration means for separating the concentrated methane gas from the biogas supplied via the flow rate adjustment means, the target concentration value of the concentrated methane concentration and the concentrated methane concentration detected by the detection means are compared and the flow rate is calculated. And a control means for performing PID control of the adjusting means, and a biogas separation and concentration system, which limits the variation of the control amount after the start of the flow rate adjusting means based on the equation (1). A limiting means for setting an upper limit value of the gas supply amount is provided.

  According to the system of the present embodiment, even if the system has a simple PID control function (for example, a system in which each parameter of PID control is fixed and a control unit having a cost of about several tens of thousands of yen), Responding to changes in biogas concentration and concentrated gas concentration that may occur due to disturbance during system operation, response control can be performed so that the separated concentrated gas concentration becomes the target concentration value without causing a hunting phenomenon or the like.

  FIG. 1 is a schematic diagram for explaining an example of a separation and concentration system in the present embodiment. In FIG. 1, reference numeral 5 denotes a limiting unit that can limit the variation of the control amount after the start based on the control amount at the start set in the control unit 4. The upper limit value of the biogas supply amount of the flow rate adjusting means 1 is set by the above limitation. The upper limit value is set by the limiting means 5 and the biogas is supplied from the flow rate adjusting means 1 controlled by the control means to the separation and concentration means 2, and the biogas is separated into methane gas and carbon dioxide gas. As a result, concentrated methane gas is obtained.

  The concentrated methane gas is led out through, for example, a back pressure valve 6, a buffer tank 7, a governor 8, and the carbon dioxide can be exhausted (permeated gas exhaust) through, for example, a vacuum pump 10 or the like. Further, the concentration detection means 3 can detect the concentration of concentrated methane through, for example, a back pressure valve 9 connected between the buffer tank 7 and the governor 8.

  Next, a description will be given in comparison with actual measurement data observed using the system shown in FIGS.

[In the case of the system of FIG. 5]
In the system of FIG. 5, as a flow rate adjusting means 1 with a maximum supply amount of 2.8 L / min (PID control amount 100%), a mass flow controller (model SEC-E40, control unit PAC-D2) manufactured by STEC Co., and as a separation and concentration means 2 Polyimide-based gas separation membrane (material 6FDA-6FAP, membrane size 12 cm ² (effective area 100 cm ² ), number of layers 32), portable gas analyzer (model CGT-7000) manufactured by Shimadzu Corporation as the concentration detection means 3, control As a means 4, a program controller (PID control amount 0 to 100%; model SYSMAC CPM2A (with PID calculation function), input / output unit CPM1A-MAD11) manufactured by OMRON Corporation, and a buffer tank 7 having a capacity of 15 L were used. The control means 4 can be easily limited on the program when outputting the PID-controlled control signal by the input / output unit (that is, density signal input (device), PID calculation (device), (Upper limit (device), control signal output (device) shall be performed in this order).

Moreover, in biogas properties (after desulfurization), methane fermentation gas generated from livestock manure is used, methane concentration is 60% to 65%, CO ₂ concentration is 35% to 40%, and water vapor is almost saturated (95% to 95% 100% RH), impurity concentration is less than 1 ppm of hydrogen sulfide.

  Then, biogas supply over time when P = 100%, I = 7%, D = 0%, control interval t = 1.0 second, target concentration value 90%, start control amount 50% The observation results of quantitative characteristics and concentrated methane concentration characteristics were examined, and the results are shown in FIG. In the case of FIG. 2, the biogas supply amount with the starting control amount of 50% is about 1.4 L / min.

  As shown in FIG. 2, the biogas supply amount characteristic and the concentrated methane concentration characteristic are stable for a predetermined time from the start of operation (in FIG. 2, elapsed time 0 to about 6 minutes). After a disturbance occurred after the passage of time (elapsed time of about 6 minutes in FIG. 2), the concentration of concentrated methane began to rise while repeating ups and downs (vibration). Then, response control is performed after a lapse of a predetermined time from the start of the increase of the concentrated methane concentration (elapsed time of about 7 minutes in FIG. 2), and the control amount after the start becomes the maximum value (100%), and the biogas supply amount is Increased.

  Thereafter, even if the concentrated methane concentration starts to decrease and reaches the target concentration value (elapsed time of about 10 minutes in FIG. 2), the state of the maximum control amount after the start (that is, the biogas supply amount reaches the maximum value). State) continued for a predetermined time (elapsed time of about 7 to 11 minutes in FIG. 2), and the concentration of concentrated methane further decreased (elapsed time of about 11 to about 16 minutes in FIG. 2).

  Then, the response control opposite to the theory shown in FIG. 4 is repeatedly performed (in FIG. 2, the elapsed time is after about 16 minutes), and the biogas supply amount does not follow the concentrated methane concentration with time. The hunting phenomenon has become large. That is, the desired response control has become difficult.

[In the case of the system in FIG. 1]
In the system shown in FIG. 1, the flow rate adjusting means 1, separation and concentration means 2, concentration detecting means 3, control means 4, and biogas properties are the same as those in the system shown in FIG. In the case of the system shown in FIG. 1, the response is too fast. In the system shown in FIG. 1, the buffer tank capacity and the control interval are changed as shown below so that the change related to the response is moderated. I took measures to do it.

  And when P = 100%, I = 5%, D = 0%, control interval t = 15 seconds, target density value 91%, starting control amount 50%, and post-start control amount variation rate 35% The observation results of biogas supply amount characteristics, concentrated methane concentration characteristics, and concentrated methane gas flow rate characteristics over time were investigated, and the results are shown in FIG. In the case of FIG. 3, the biogas supply amount at the start control amount of 50% is 1.4 L / min, and the upper limit value of the biogas supply amount is “2.8 × (50% + (50 % × 35%)) ”, which is about 1.9 L / min.

  As shown in FIG. 3, the biogas supply amount characteristic, the concentrated methane concentration characteristic, and the concentrated methane gas flow rate characteristic are stable for a predetermined time from the start of operation (in FIG. 3, elapsed time 0 to about 70 minutes). However, after the occurrence of the disturbance after the lapse of the predetermined time (elapsed time of about 70 minutes in FIG. 3), the concentration of the separated and concentrated methane gas began to repeatedly increase and decrease (vibrates). Then, response control was started after a lapse of a predetermined time from the start of the increase of the concentrated methane concentration (elapsed time of about 71 minutes in FIG. 3), and a hunting phenomenon occurred.

  Next, after the response control for the predetermined time (the elapsed time in FIG. 3 is about 100 minutes), the control amount after the start is increased (that is, the biogas supply amount is increased so as to become the maximum value), and the hunting phenomenon is caused. Despite the tendency to become larger, the biogas supply amount was maintained at the upper limit (about 1.9 L / min). Then, after the holding state has elapsed for a predetermined time (the elapsed time in FIG. 3 is about 120 minutes), the hunting phenomenon is eliminated, the concentrated methane concentration is maintained at the target concentration value, and desired response control is continued. (Elapsed time after about 160 minutes in FIG. 3).

  From the results shown above, by setting the upper limit as in the system of FIG. 1, even if the biogas concentration or the concentrated gas concentration is changed due to disturbance or the like and the hunting phenomenon is caused, the hunting phenomenon is promptly performed. It has been found that response control (controlling the flow rate adjusting means and adjusting the biogas supply amount) can be performed so that the concentrated gas concentration becomes the target concentration value. Further, it can be read that the hunting phenomenon can be easily resolved more quickly by setting the rate of fluctuation not to be too large (for example, set to 35% or less). For example, it can be read that a more preferable result is obtained when the upper limit value is set to 10% or less in the embodiment.

  Therefore, according to the present embodiment, it has been found that even if a hunting phenomenon that is difficult to be solved by the conventional system is induced, the hunting phenomenon can be quickly eliminated and the intended response control can be performed.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

  For example, in the embodiment, an example of a system using various devices such as a back pressure valve, a buffer tank, and a governor 8 has been described. However, separation and concentration means for separating concentrated methane gas from biogas supplied via the flow rate adjustment means 1 2, a control means 4 for comparing and calculating the target concentration value of the concentrated methane concentration and the concentrated methane concentration detected by the detecting means 3 to perform PID control of the flow rate adjusting means 1, and the flow rate adjustment based on the above equation (1) If the separation / concentration system for biogas is provided with the limiting means 5 for limiting the fluctuation of the control amount after the start of the means and setting the upper limit value of the biogas supply amount, the various devices are omitted or added as appropriate Even so, it is clear that the same effect as the embodiment can be obtained. For example, any separation / concentration means may be used as long as it has a gas separation membrane and can separate concentrated methane gas from biogas, and the shape, material, configuration (number, arrangement, etc.) of the gas separation membrane are not limited. Absent.

  In the embodiment, the case where the variation rate of the control amount after start is set to 35% has been described. However, the variation rate is not limited to 35%, and is limited based on the equation (1) as described above. Any numerical value can be set as appropriate.

  Further, the separation and concentration system can constitute, for example, a well-known CPU, ROM, RAM, computer having an I / O interface, keyboard, display, external memory, printer, etc. in each means, and a part of each device. Alternatively, all functions can be configured by a computer program, and the program can be executed using the computer to realize the present invention. Each step of the system is configured by a computer program, and the program is Needless to say, the present invention can be implemented by using a computer.

  In the measured data in FIGS. 2 and 3, there is a time zone in which the behavior at the time of occurrence of the disturbance shows an operation different from the theory of FIG. The description of FIG. 4 only shows the relationship between the biogas supply amount and the concentration of the concentrated gas in the steady state, and the type of disturbance (for example, clogging of each pipe due to moisture, the malfunction of the concentration detection means, the separation concentration means) The response time (time constant) may vary greatly depending on the (apparatus) internal gas flow fluctuations, and operations that cannot be explained in FIG. 4 may occur.

Schematic explanatory drawing which shows an example of the separation concentration system in this embodiment. The characteristic view which shows the simulation result of the system of FIG. The characteristic view which shows the simulation result of the system of FIG. The characteristic figure of the relationship between the amount of mixed gas passage (biogas supply amount) per unit time and concentrated gas concentration in a gas separation membrane. Schematic explanatory drawing which shows an example of the separation / concentration system for common biogas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flow volume adjustment means 2 ... Separation concentration means 3 ... Concentration detection means 4 ... Control means 5 ... Restriction means

Claims (3)

A separation and concentration means for separating concentrated methane gas from biogas with a gas separation membrane;
Flow rate adjusting means for adjusting the amount of biogas supplied to the separation and concentration means;
Detection means for detecting the methane concentration of the concentrated methane gas obtained by the separation and concentration means;
The biogas supply amount at the start of operation of the flow rate adjusting means is set in correspondence with the target concentration value of the methane concentration, the target concentration value is compared with the detection result by the detection means, and based on the calculation result Control means for PID-controlling the flow rate adjusting means so that the methane concentration becomes a target concentration value;
The fluctuation rate of the PID control amount P _t after the start of operation based on the PID control amount P ₀ at the start of the operation is defined as W, and the following formula (where 0 ≦ P _t , P ₀ , W ≦ 100%) , P _t + (P ₀ × W) <100%), limiting means for limiting the fluctuation of the PID control amount P _t and setting the upper limit value L of the biogas supply amount;
A separation / concentration system for biogas, characterized by comprising:
L = “Biogas supply amount when P _t = 100%” × (P _t + (P ₀ × W))   The separation / concentration system for biogas according to claim 1, wherein each parameter of PID control in the control means is fixed.   The separation / concentration system for biogas according to claim 1, wherein the fluctuation rate W is 35% or less.

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