JP5598245B2 - Acid gas treatment method - Google Patents

Description

  The present invention relates to a method for treating acidic gases such as harmful hydrogen chloride and sulfur oxide generated in combustion facilities such as municipal waste waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories. Specifically, the present invention relates to a method for efficiently controlling the addition amount of an alkaline agent for treating acid gas.

  Exhaust gas containing harmful hydrogen chloride and sulfur oxide is treated with an alkaline agent such as slaked lime or baking soda, and then removed by a dust collector such as a bag filter (BF), and then discharged from the chimney. On the other hand, the fly ash collected by the dust collector contains harmful heavy metals such as Pb and Cd, and is disposed of in landfill after stabilizing these harmful heavy metals.

  Sodium bicarbonate finely processed to 5 to 30 μm, which is an alkaline agent for treating acid gas, has higher reactivity than slaked lime, can stably treat acid gas, has less unreacted content, and can reduce the amount of landfill disposal. This is an effective means for reducing the load. In addition, heavy metals are generally treated by insolubilization with a chelate such as diethyldithiocarbamate, and the effect of fixing heavy metals is high in the short term. The problem of re-elution of heavy metals such as lead due to decomposition remains. On the other hand, heavy metal fixation with phosphoric acid compounds such as phosphoric acid is a highly valuable treatment method from the viewpoint of environmental protection, because it changes to the form of hydroxyapatite, which is an inorganic mineral, and has excellent long-term stability at the final disposal site. . Further, the method of treating fly ash treated with fine powdered sodium bicarbonate with a heavy metal fixing agent such as phosphoric acid is an effective means having many environmental load reducing effects.

  By the way, controlling the addition amount of alkaline agents such as slaked lime and baking soda that treat acidic gases such as hydrogen chloride and sulfur oxides not only reduces the cost of treating acidic gases, but also reduces the unreacted content of alkaline agents. The effect of reducing fly ash landfill disposal can be expected.

  The amount of alkali agent added to treat acidic gases such as hydrogen chloride and sulfur oxide is generally based on the concentration of hydrogen chloride measured with an ion electrode type hydrogen chloride measuring device installed after the bag filter. The feedback control is performed by the PID control device. However, in a combustion facility such as an incineration facility, a device for measuring the concentration of acidic gas at the entrance is usually not installed, and PID control parameters are set and the control output is adjusted without knowing the state of fluctuation at the entrance. However, the PID control device has five setting items of P, I, D, addition amount (output) lower limit and addition amount (output) upper limit, and the setting value of each item is combined to determine the control output value. It takes a lot of time to study the addition control. For this reason, in general, the setting by the PID control apparatus has many facilities that perform control in which the amount of addition is greatly increased when the control target value (SV) is exceeded.

  However, the control output of a normal PID control device can only set a single upper limit. For example, when the control target value (SV) of the HCl concentration is set to 40 ppm, the single upper limit of the control output at a concentration of 40 ppm or more. As a result, the alkali agent is added to the limit, causing excessive addition of the alkali agent. The feedback control is affected by measurement delay of the acid gas measuring device. The hydrogen chloride concentration at the bag filter outlet is usually measured by an ion electrode method (for example, HL-36 manufactured by Kyoto Electronics Industry), and the sulfur oxide concentration is measured by an infrared absorption method (for example, NSA-3080 manufactured by Shimadzu Corporation). Including the sampling time of the sample exhaust gas and the response time of the measuring instrument, there is a great measurement delay of 5 to 10 minutes. This measurement delay causes an addition lag of the alkaline agent, leading to poor processing of the acid gas and causing excessive addition of the alkaline agent.

  Various control methods have been studied in order to solve this problem. Patent Document 1 proposes “P + PID control” in which P is further added to a normal PID control expression. This proposal is intended to cope with the sudden generation of acidic gas, which is difficult with normal PID control. In Patent Documents 2 and 3, feedforward control for determining the addition amount of the alkaline agent based on the acidic gas concentration at the inlet, and the addition amount of the alkaline agent based on the acidic gas concentration after the alkaline agent has been processed. A control method that combines feedback control that compensates for this problem has been proposed. This control method is expected to have an effect of suppressing the excessive addition of feedback control, and an effect of reducing the acid gas stabilization treatment and the excessive addition of the alkaline agent is obtained.

JP 2002-113327 A Japanese Patent Laid-Open No. 10-165552 JP 2006-75758 A

  However, in Patent Document 1, it is possible to cope suddenly with the entrance to some extent, but the measurement delay of the measuring device is not taken into account, and it is possible to deal with the acid gas processing failure due to the addition lag of the alkaline agent due to the measurement delay. Can not do it. In Patent Documents 2 and 3, in the combustion facilities such as incineration facilities, most of the facilities measure only the acidic gas concentration at the outlet, and in order to implement this control method, the acidic gas at the inlet is used. It is necessary to introduce a new and expensive acid gas measuring device for measuring the concentration.

  In consideration of the above-described conventional technology, the present invention suppresses generation of acidic gas and excessive addition of an alkaline agent due to measurement delays of conventional feedback control in a feedback format that does not require the introduction of a new and expensive acidic gas measuring device. An object is to provide an acid gas treatment method.

  (1) In an acidic gas treatment method in which the addition amount of an alkaline agent is feedback controlled based on a measurement signal of an acidic gas measuring device installed in a process after adding the alkaline agent to the acidic gas contained in combustion exhaust gas, at least 2 Setting a range of slopes of two acidic gas concentrations (for example, a 6-second average of the latest HCl concentration slopes described later is a positive range and a negative range), and acidic gas for each of the at least two slope ranges A step of setting a concentration control target value (for example, 30 ppm, 40 ppm, etc. in Example 1 to be described later), and a control output value indicating the addition amount of the alkaline agent based on at least the measurement signal and the control target value are calculated. And the step of setting the control target value has a large slope of the acidic gas concentration (for example, the latest H described later) The control target value to be set when the 6-second average of the l-concentration slope is positive (when the acid gas tends to increase) is set when the range of the acid gas concentration slope is small (for example, the latest HCl concentration slope described later) This is characterized by being smaller than the control target value set when the 6-second average is negative (when acid gas is decreasing).

  In the conventional PID control, for example, when the control target value (SV) of the acid gas concentration is set to 40 ppm, the control output increases after reaching 40 ppm, the alkali agent is added, and the added alkali agent reacts with the acid gas. As a result, the control output decreases after the acid gas concentration reaches 40 ppm or less. Therefore, the tendency of increase / decrease in acid gas concentration has not been considered.

  On the other hand, according to (1), the acid gas concentration control target value when the acid gas is increasing tends to be smaller than the acid gas concentration target value when the acid gas is increasing. The control output value becomes larger than the control output value when acid gas is decreasing.

  (2) In the acidic gas treatment method according to (1), the lower limit value of the control output value indicating the addition amount of the alkaline agent (for example, LO [control output lower limit] (fine powder in FIGS. 15, 17, and 19 described later) Between the acid gas concentration (for example, the minimum addition amount of baking soda) and the upper limit value (for example, LO [control output upper limit] (maximum addition amount of fine baking soda) in FIGS. 15, 17, and 19 to be described later)). Corresponding to the BF outlet HCl concentration in FIGS. 15, 17, and 19 to be described later, a new upper limit value of the control output value (for example, the control output addition amount in FIGS. 15, 17, and 19 to be described later) is set. A method for treating acid gas, further comprising a step of setting one or more.

  A normal PID control device has only one control output upper limit. For example, if the control target value (SV) of the acid gas is constant, the alkaline agent is added up to the upper limit value regardless of the size of the acid gas concentration. Therefore, excessive addition is caused. On the other hand, according to (2), by adding a restriction on the control output according to the current acid gas concentration (step control method to be described later), an appropriate addition of an alkaline agent according to the size of the acid gas concentration Therefore, the amount of addition can be reduced.

  (3) The acidic gas treatment method according to (1) or (2), wherein the acidic gas measuring device is a hydrogen chloride concentration measuring device by an ion electrode method.

  (4) The acid gas treatment method according to any one of (1) to (3), wherein the acid gas measurement device is a sulfur oxide concentration measurement device by an infrared absorption method or an ultraviolet fluorescence method. Method.

  The acidic gas measuring device used in the present invention can be implemented regardless of the measuring method. The hydrogen chloride concentration can be measured by an ion electrode method, single absorption line absorption spectroscopy using a laser, or the like, and sulfur oxide can be measured by an infrared absorption method, an ultraviolet fluorescence method, or the like. Since the main purpose of the present invention is to improve the measurement delay of acid gas, it uses a hydrogen chloride measurement device based on the ion electrode method or a sulfur oxide measurement device based on the infrared absorption method or ultraviolet fluorescence method, which has a large measurement delay. It is especially effective in facilities that measure the acidic gas after the bag filter and perform feedback control.

  In addition, there is a possibility that the excessive addition of feedback control can be improved by measuring the hydrogen chloride concentration after the bag filter in the combustion facility in a laser form without measurement delay and performing feedback control. However, the laser method has not been widely used as a measuring device that leaves a technical problem in JIS certification and determines the concentration of acid gas in the final exhaust gas.

  (5) The acidic gas treatment method according to any one of (1) to (4), wherein the slope of the acidic gas concentration for setting the control target value is an average value within the latest 7 minutes.

  It is desirable to use the average value within the last 7 minutes as the slope of the acidic gas concentration that sets the control target value. When the average value of the inclination of the acid gas within 7 minutes is used, an appropriate selection can be made and the acid gas can be treated stably.

  (6) In the acid gas treatment method according to any one of (1) to (5), the amount of alkali agent added using both the control output calculated from the hydrogen chloride concentration and the control output calculated from the sulfur oxide concentration It is characterized by controlling.

  In combustion facilities of industrial waste incinerators and private factories, hydrogen chloride and sulfur oxides are often generated at high concentrations. In this case, both hydrogen chloride and sulfur oxide are treated, and the control output and sulfur oxide concentration obtained based on the hydrogen chloride concentration of the hydrogen chloride concentration measuring device provided at the back of the bag filter are also included. For example, both the hydrogen chloride and sulfur oxide acidic gases can be treated stably by adding the control outputs obtained in the above.

  (7) In the acidic gas processing method as described in (1) thru | or (6), the alkaline agent which processes acidic gas is the fine powder baking soda whose average particle diameter is 5-30 micrometers, The processing method of acidic gas characterized by the above-mentioned. .

The alkaline agent used in the present invention is preferably finely powdered baking soda having an average particle diameter that is particularly fast with an acid gas and adjusted to 5 to 30 μm. Since the reactivity of the fine powdered baking soda is fast, the control responsiveness is good and the performance of the present invention can be exhibited effectively. However, the present invention is based on a control method and can be applied to slaked lime. The slaked lime can exhibit the performance of the present invention when it is a high specific surface area slaked lime having a high specific surface area of 30 m ² / g or more, which is highly reactive with acid gas.

  According to the present invention, in a feedback type that does not require the introduction of a new and expensive acid gas measuring device, it is possible to improve the processing failure of the acid gas due to the measurement delay of the acid gas measuring device that the conventional feedback control has and to add an excessive amount of alkaline agent. Reduced and efficient acid gas addition enables stable treatment of acidic gas.

It is a block diagram showing the structure of the acidic gas processing system 1 which adds fine powder baking soda to HCl which is waste gas in incineration facilities. 1 is a basic configuration diagram of a simulation reaction system 1. FIG. It is a graph which shows the relationship between fine powder baking soda addition equivalent and HCl removal rate. It is a graph which shows the behavior of bag filter exit HCl concentration of a real machine. It is a graph which shows the behavior of the bag filter exit HCl concentration of the simulation reaction system 1. 2 is a basic configuration diagram of a simulation reaction system 2. FIG. It is a graph which shows the relationship between fine powder baking soda addition equivalent and HCl removal rate in exhaust gas reaction. It is a graph which shows the relationship between fine powder baking soda addition equivalent and HCl removal rate in reaction on a bag filter. It is a graph which shows the behavior of the bag filter exit HCl concentration of the simulation reaction system 2. It is a table | surface which shows the bag filter exit HCl density | concentration etc. for every comparative example and an Example. It is a graph which shows the behavior of inlet HCl concentration. 5 is a graph showing the behavior of the amount of fine powdered sodium bicarbonate added and the outlet HCl concentration in Comparative Example 1. 4 is a graph showing the behavior of the amount of fine powdered baking soda added and the concentration of outlet HCl in Example 1. It is a graph which shows the behavior of the fine sodium bicarbonate addition amount in Example 2, and an exit HCl concentration. 10 is a table of control settings for a step control method in Comparative Example 2. It is a graph which shows the behavior of the addition amount of fine powder sodium bicarbonate and the outlet HCl concentration in Comparative Example 2. 10 is a table of control settings for a step control method according to the third embodiment. It is a graph which shows the behavior of the fine sodium bicarbonate addition amount in Example 3, and an exit HCl concentration. It is a table | surface of the control setting of the step control system in Example 4 grade | etc.,. It is a graph which shows the behavior of the fine sodium bicarbonate addition amount in Example 4, and an outlet HCl density | concentration. It is a graph which shows the behavior of the fine powder sodium bicarbonate addition amount in Example 5, and an exit HCl concentration. It is a graph which shows the behavior of the fine sodium bicarbonate addition amount and the outlet HCl concentration in Example 6. It is a graph which shows the behavior of fine powder baking soda addition amount and exit HCl concentration in Example 7. It is a graph which shows the behavior of the fine sodium bicarbonate addition amount in Example 8, and the exit HCl concentration.

  Hereinafter, the present invention will be described more specifically with reference to embodiments, but the present invention is not limited thereto.

  FIG. 1 is a block diagram showing the configuration of an acidic gas treatment system 1 that adds fine powdered baking soda to HCl that is an exhaust gas in an incineration facility.

  The acid gas treatment system 1 includes a control device 11, a fine powder baking soda addition device 12, a bag filter 13, and an HCl measurement device 14. The control device 11 calculates the control output value of the fine powdered sodium bicarbonate addition amount by the PID control method based on the HCl concentration measurement signal or the like. The fine powdered sodium bicarbonate adding device 12 adds fine powdered sodium bicarbonate to HCl in the exhaust gas based on the control output value of the fine powdered sodium bicarbonate added amount calculated by the control device 11.

  The bag filter 13 removes dust after the reaction between HCl in the exhaust gas and fine baking soda. The HCl measuring device 14 is configured so that fine baking soda accumulated on the bag filter 13 (fine baking soda remaining by reaction with HCl in the exhaust gas is accumulated on the bag filter 13) and HCl after the exhaust gas reaction have reacted. The HCl concentration (bag filter outlet HCl concentration described later) is measured, and an HCl concentration measurement signal is transmitted to the control device 11.

  The acidic gas treatment system 1 repeats such a cycle and performs feedback control, so that the control device 11 performs control to make the control output value of the added amount of fine powder sodium bicarbonate appropriate.

  The HCl concentration measuring device 14 is an ion electrode type hydrogen chloride concentration measuring device.

  Further, as shown in FIG. 1, an HCl concentration measuring device is used to measure the HCl concentration (bag filter outlet HCl concentration described later) after the fine baking soda accumulated on the bag filter 13 reacts with HCl after the exhaust gas reaction. 14 is preferably installed. This is because fine powdered sodium bicarbonate remaining due to the reaction with HCl in the exhaust gas is accumulated on the bag filter 13, and this accumulated fine powdered sodium bicarbonate reacts with HCl after the exhaust gas reaction, so the HCl concentration can be measured more accurately. Because.

  The installation of the HCl concentration measuring device 14 is not limited to the above, and any step can be used as long as it is a step after adding the fine powdered sodium bicarbonate added by the fine powdered sodium bicarbonate addition device 12 to the HCl in the exhaust gas. Also good.

  Further, the control performed by the control device 11 will be described in detail.

  The control device 11 provides two ranges, a positive range and a negative range, for the gradient of HCl concentration (concentration change rate with time). Then, a control target value of HCl concentration is set for each of these two ranges.

  Here, the control target value for the HCl concentration is set such that the control target value provided for the positive range of the HCl concentration is smaller than the control target value for the negative range. By doing in this way, the control output value of the fine powder sodium bicarbonate addition amount when the HCl concentration tends to increase can be made larger than the control output value when the HCl concentration tends to decrease.

  In addition, when the HCl concentration tends to decrease, the amount of fine powdered sodium bicarbonate added may be directly reduced by executing a control to increase the output value of the amount of fine powdered sodium bicarbonate to 0.7 times, for example. By doing in this way, when the HCl concentration tends to decrease, the amount added can be quickly reduced, and excessive addition can be reduced.

  Next, the control method in the control device 11 is changed to the PID control method, and the step control method will be described.

  The step method is a control method in which a control output corresponding to the HCl concentration is set stepwise. Specifically, in addition to the upper limit value of the control output value set in the PID control method, a new upper limit value of the control output value is set corresponding to the HCl concentration.

  Here, in normal PID control, since there is only one upper limit of the amount of fine powdered sodium bicarbonate added, fine powdered sodium bicarbonate is added within the range reaching the upper limit value regardless of the HCl concentration. Is caused. Therefore, by adopting a step control system, by adding a new control output upper limit value according to the current HCl concentration, it becomes possible to add an alkali agent appropriately according to the size of the acid gas concentration. It is possible to suppress excessive addition of.

  Here, a new control output upper limit value is set corresponding to the HCl concentration. However, the higher the HCl concentration, the higher the new control output upper limit value is set. However, in order to suppress the excessive addition of the alkaline agent, from the upper limit value of the control output value set in the PID control method (for example, LH [control output upper limit] in FIGS. 15, 17 and 19 described later). A small value is preferable.

  As an example of setting a new control output upper limit value, the higher the HCl concentration, the higher the control output addition amount corresponding to the BF outlet HCl concentration [calculated input value] described in FIG. 15, FIG. 17 and FIG. It is preferable that the new control output upper limit value is also set high.

  The acid gas measuring device used in the present embodiment is not limited to the hydrogen chloride (HCl) concentration measuring device (HCl measuring device 14), and may be a sulfur oxide concentration measuring device using an infrared absorption method or an ultraviolet fluorescence method. .

  In this embodiment, the slope of the acidic gas concentration that sets the control target value for the HCl concentration is the average value within the last 7 minutes. This is because when an average value of the inclination of the acidic gas within 7 minutes is used, an appropriate selection can be made and the acidic gas can be treated stably.

  In this embodiment, only the control output calculated from the hydrogen chloride is used. However, the alkaline agent using both the control output calculated from the hydrogen chloride concentration and the control output calculated from the sulfur oxide concentration is used. The amount added may be controlled. This is because hydrogen chloride and sulfur oxides are often generated at high concentrations in industrial waste incinerators and combustion facilities of private factories.

  In this case, both hydrogen chloride and sulfur oxide are treated, and the control output and sulfur oxide concentration obtained based on the hydrogen chloride concentration of the hydrogen chloride concentration measuring device provided at the rear stage of the bag filter are also included. For example, both the hydrogen chloride and sulfur oxide acidic gases can be treated stably by adding the control outputs obtained in the above.

  The fine baking soda used in the present embodiment is preferably fine baking soda having an average particle diameter of 5 to 30 μm, which is particularly fast in reactivity with acidic gas. This is because the control responsiveness is good because the reactivity of fine powdered baking soda is fast.

  In the present embodiment, fine powder baking soda is used as the alkaline agent, but there is no particular limitation on the alkaline agent that exhibits the effect of the present embodiment. Examples of the alkali agent other than fine powdered sodium bicarbonate include sodium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium sesquicarbonate, natural soda, sodium hydroxide, potassium hydroxide, magnesium oxide, magnesium hydroxide and the like. When the alkaline agent is a powder, a fine powder having a particle size with a high reactivity with an acid gas of less than 30 μm, particularly 5 to 20 μm is preferable. An agent having a particle size adjusted in advance may be applied, or a pulverization facility may be provided on site, and an alkaline agent having a coarse particle size may be added while being crushed on site.

  In addition, in a combustion facility that measures acidic gas at the inlet, it is also an effective means to perform feedback control with this control method in addition to feedforward control. Furthermore, when a denitration catalyst facility is installed in the rear stage of the bag filter, it is necessary to apply it at around 200 ° C. Therefore, the thermal loss of reheating energy can be reduced by adjusting the bag filter temperature to 180 to 230 ° C. Economical operation is possible.

[Test Example 1]
A simulation reaction system was created from the results of actual machine studies. First, the simulation reaction system 1 will be described as a first pattern. In addition, the actual machine examination result measured in the municipal waste incineration facility by the ion electrode method using the PID apparatus which is a conventional control for fine powder baking soda (Hypercer B-200 manufactured by Kurita Kogyo Co., Ltd.) adjusted to an average particle size of 8 μm (Kyoto) This is feedback-controlled based on the concentration of hydrogen chloride produced by Denki Kogyo HL-36).

[Simulation Reaction System 1]: Assuming Reaction in Exhaust Gas In examining the simulation reaction system 1, the reaction of sodium bicarbonate and hydrogen chloride (HCl) is an instantaneous reaction in the exhaust gas, and the simulation reaction system 1 is shown in FIG. Configured.

The basic configuration of the simulation reaction system 1 will be described with reference to FIG.
The chemical injection control in the incineration facility is based on the calculation of the control expression such as PID based on the HCl concentration (after treatment) signal of the ion electrode type HCl concentration measuring device installed at the bag filter outlet (addition amount of fine sodium bicarbonate ( Ag)) is determined, and the determined addition amount of fine baking soda (acid gas treating agent) is added to the exhaust gas (inlet HCl concentration (Hi)). Fine powder baking soda added to the flue reacts with an acidic gas such as HCl in the exhaust gas to remove HCl in the exhaust gas (removed based on the HCl removal rate (α)). The bag filter outlet HCl concentration (Ho) after this reaction is measured with an ion electrode type HCl measuring device, but the measurement delay due to the facility, the measurement delay due to the exhaust gas sampling, and the measurement delay due to the ion electrode type measurement (response time) Yes, a feedback-specific control delay occurs. Therefore, the measurement delay time (T) of HCl in this simulation was set as the following formula (1).

T = T1 + T2 + T3 (1)

T: Measurement delay time of simulation reaction system T1: Facility delay time (sec) [30 sec setting]
T2: Exhaust gas sampling time of the HCl measuring device (sec) [240 sec setting]
T3: 90% response time (sec) of HCl measuring device [180 sec setting]

  In addition, since 90% response time (measurement delay) of the ion electrode type is affected by diffusion of HCl gas into the absorbing solution, T3 is set to the following formula (2). In this simulation examination, the measurement delay time of this simulation was set as T1 = 30 seconds, T2 = 240 seconds, and T3 = 180 seconds from the situation of the facility.

T3 = 2.3 × τ (2)

_{Y n = Y n-1 +} (X n -Y n-1) ÷ τ × Ts (3)

τ: Time constant (sec)
Ts: Unit simulation time (= data sampling time) (sec) [0.5 sec setting]
X _n : Current measuring device input HCl concentration (ppm)
Y _n : Current measuring device output HCl concentration (ppm)
Y _n-1 : HCl concentration (ppm) output from the measuring device of the previous [before Ts (sec)]

  Further, the HCl removal rate (α) of the inlet HCl concentration (Hi) by fine powdered baking soda was calculated from the relationship between the fine powdered sodium bicarbonate addition equivalent (J) and the HCl removal rate (FIG. 3) from the application knowledge of fine powdered baking soda manufactured by Kurita Kogyo. The reaction between HCl concentration and fine powdered sodium bicarbonate was instantaneous. In addition, fine powder baking soda addition equivalent (J) is computed by following formula (4).

J = Ag ÷ {Hi ÷ 0.614 ÷ 1000 ÷ M1 × M2 × F ÷ 1000} (4)

J: Fine powder baking soda addition equivalent Ag: Fine powder sodium bicarbonate addition amount (kg / h)
Hi: Inlet HCl concentration (ppm)
M1: HCl molecular weight [set at 36.5]
M2: Sodium bicarbonate molecular weight [set at 84]
F: amount of exhaust gas ^(Nm 3 / h) [set by 25,000Nm ³ / h]

  Based on this theory, the same PID control conditions as the actual machine to which fine baking soda was added “P (proportional gain) = 10%, I = 0.1 seconds, D = 0.1 seconds, additive output lower limit 5 kg / h, additive amount As a result of the simulation with the “output upper limit 100 kg / h”, the behavior of the outlet HCl concentration (Ho) was different between the simulation and the actual machine (FIGS. 4 and 5). The outlet HCl concentration (Ho) is calculated by the following equation (5).

Ho = Hi × (1−αg ÷ 100) (5)

Hi: Inlet HCl concentration (ppm)
Ho: HCl concentration at the outlet of the bag filter (ppm)
α: HCl removal rate (%) [set from the relationship between added equivalent and HCl removal rate (FIG. 3)]

  Comparing the transition of the HCl concentration after the HCl treatment with the addition of fine baking soda, the increase rate of the HCl concentration in the simulation reaction system 1 is faster than that in the actual machine. Although the above parameters such as measurement delay time were changed and examined, the results of the actual machine and the simulation did not match. Therefore, the reason why the HCl concentration increase rate in the actual machine is slower than that in the simulation reaction system 1 is considered that unreacted fine baking soda collected by the bag filter is reacting with HCl.

[Test Example 2]
Next, the simulation reaction system 2 will be described as a second pattern.

[Simulation reaction system 2]: Combined reaction on exhaust gas and bag filter From the above examination results, taking into account the reaction between unreacted fine baking soda on the bag filter and HCl, in addition to the reaction in the exhaust gas, The reaction was configured as shown in FIG. Moreover, the residence time of the collected matter in the bag filter is usually about 2 hours. Therefore, in this simulation reaction system 2, the fine baking soda on the bag filter disappears in a specified time (set in about 2 hours).

The basic configuration of the simulation reaction system 2 will be described with reference to FIG.
First, in chemical injection control at an incineration facility, the amount of added chemical (addition of fine baking soda) is calculated by the control formula such as PID based on the HCl concentration (after treatment) signal of the ion electrode type HCl concentration measuring device installed at the bag filter outlet. Amount (Ag)) is determined, and the determined addition amount of fine baking soda (acid gas treating agent) is added to the exhaust gas (inlet HCl concentration (Hi)).

  The HCl concentration (Hg) after reaction in the exhaust gas is derived from the fine powdered sodium bicarbonate addition equivalent (Jg) of the exhaust gas reaction and the exhaust gas reaction HCl removal rate (αg) (the following formula (6)). In addition, the fine powder baking soda addition equivalent (Jg) of exhaust gas reaction is computed by following formula (7).

Hg = Hi × (1−αg ÷ 100) (6)

Hi: Inlet HCl concentration (ppm)
Hg: HCl concentration after exhaust gas reaction (ppm)
αg: HCl removal rate in exhaust gas reaction (%)
[Set from the relationship between the exhaust gas reaction fine powder baking soda addition equivalent and HCl removal rate (Fig. 7)]

Jg = Ag ÷ {Hi ÷ 0.614 ÷ 1000 ÷ M1 × M2 × F ÷ 1000} (7)

Jg: Exhaust gas reaction fine powder baking soda addition equivalent Ag: Fine powder sodium bicarbonate addition amount (kg / h)
Hi: Inlet HCl concentration (ppm)
M1: HCl molecular weight [set at 36.5]
M2: Sodium bicarbonate molecular weight [set at 84]
F: amount of exhaust gas ^(Nm 3 / h) [set by 25,000Nm ³ / h]

  Moreover, the fine baking soda remaining by the exhaust gas reaction accumulates on the bag filter as needed. The fine baking soda accumulated on the bag filter reacts with HCl after the exhaust gas reaction, and the HCl concentration (Ho) at the bag filter outlet is determined. At this time, the amount of fine baking soda accumulated on the bag filter (As) was obtained by subtracting the amount of fine baking soda reacted with HCl on the bag filter from the fine baking soda accumulated in the exhaust gas reaction.

  Also, the HCl removal rate (αs) on the bag filter is calculated from the amount of fine powdered sodium bicarbonate added on the bag filter (Js) calculated from the amount of fine powdered sodium bicarbonate accumulated on the bag filter (As) and the HCl concentration after the exhaust gas reaction (Hg). The HCl concentration (Ho) at the bag filter outlet was determined (the following formula (8)). In addition, the fine powder baking soda addition equivalent (Js) on a bag filter is computed by following formula (9). The delay in HCl measurement was set to T (= T1 + T2 + T3) as in the simulation reaction system 1.

Ho = Hg × (1−αs ÷ 100) (8)

Hg: HCl concentration after exhaust gas reaction (ppm)
Ho: HCl concentration at the outlet of the bag filter (ppm)
αs: HCl removal rate of the reaction on the bag filter (%)
[Set from the relationship between the equivalent weight of fine powdered sodium bicarbonate on the bag filter and the HCl removal rate (Fig. 8)]

Js = As ÷ {Hg ÷ 0.614 ÷ 1000 ÷ M1 × M2 × F ÷ 1000} (9)

Js: Equivalent amount of fine baking soda on bag filter As: Amount of fine baking soda on bag filter (kg / h)
Hg: HCl concentration after exhaust gas reaction (ppm)
M1: HCl molecular weight [set at 36.5]
M2: Sodium bicarbonate molecular weight [set at 84]
F: amount of exhaust gas ^(Nm 3 / h) [set by 25,000Nm ³ / h]

As = Z _n ÷ Ts × 3600 (10)

Z _n : Accumulated amount of baking soda on bag filter (kg)
Ts: Unit simulation time (= data sampling time) (sec)
[0.5 sec setting]

_{Z n = Z n '× (} 1-2.3 ÷ T4 × Ts) (11)

Z _{n ′} : Unreacted fine baking soda amount (kg)
T4: Accumulated fine powder baking soda on bag filter 90% extinction time constant (sec)
[7,200sec setting]
Ts: Unit simulation time (= data sampling time) (sec)
[0.5 sec setting]

Z _{n ′} = (Ag ÷ 3600 × Ts−Rg) + (Z _n−1 −Rs) (12)

Ag: Fine powder baking soda addition amount (kg / h)
Ts: Unit simulation time (= data sampling time) (sec)
[0.5 sec setting]
Rg: sodium bicarbonate reaction amount in exhaust gas reaction (kg / h)
Z _n-1 : Accumulated amount of fine baking soda on the bag filter before Ts (Sec) (kg)
Rs: Amount of sodium bicarbonate reaction in bag filter reaction (kg / h)

Rg = (Hi ÷ 0.614 ÷ 1000 ÷ M1 × M2 × F ÷ 1000) ÷ 3600 × Ts × αg ÷ 100 (13)

Hi: Inlet HCl concentration (ppm)
M1: HCl molecular weight [set at 36.5]
M2: Sodium bicarbonate molecular weight [set at 84]
F: amount of exhaust gas ^(Nm 3 / h) [set by 25,000Nm ³ / h]
αg: HCl removal rate in exhaust gas reaction (%)

Rs = (Hg ÷ 0.614 ÷ 1000 ÷ M1 × M2 × F ÷ 1000) ÷ 3600 × Ts × αs ÷ 100 (14)

Hg: HCl concentration after exhaust gas reaction (ppm)
M1: HCl molecular weight [set at 36.5]
M2: Sodium bicarbonate molecular weight [set at 84]
F: amount of exhaust gas ^(Nm 3 / h) [set by 25,000Nm ³ / h]
αs: HCl removal rate of the reaction on the bag filter (%)

  In this theory, as a result of performing a simulation by changing the HCl removal rate due to the reaction in the exhaust gas and the reaction on the bag filter, the exhaust gas reaction and the reaction on the bag filter are equivalent to the HCl removal rate [95% exhaust gas reaction, The reaction on the bag filter 75%] almost coincided with the behavior of the bag filter outlet HCl concentration in the actual machine (FIG. 4) (FIG. 9). This is a result confirming that the rate of HCl increase is mitigated because fine baking soda on the bag filter reacts with HCl. In this simulation, the reaction with HCl on the bag filter is inferior to the exhaust gas reaction. This is presumably because the reaction on the bag filter has a low HCl removal rate because the HCl concentration to be treated is lower than the exhaust gas reaction. Moreover, it is thought that the fine powder baking soda accumulate | stored in a bag filter is thermally decomposed into the sodium carbonate by the temperature of waste gas. The HCl removal rate of sodium carbonate is inferior to that of fine baking soda, so the removal rate on the bag filter may have decreased.

  From the results of this study, it is considered that the reaction of fine baking soda and HCl in the combustion exhaust gas is a reaction system in which the reaction in the exhaust gas and the reaction of fine baking soda accumulated on the bag filter are combined. Further, since the behavior of the HCl concentration at the bag filter outlet almost coincided with the actual machine, it can be seen that the simulation reaction system 2 is effective as a tool for evaluating a control method using fine powdered sodium bicarbonate.

The results of examining various control methods in the simulation reaction system 2 are shown below.
In addition, the average particle diameter of the fine powder baking soda used in the following Examples 1-8 is 5-30 micrometers. Moreover, the HCl measuring device 14 used in Examples 1-8 is a hydrogen chloride concentration measuring device by the ion electrode method.

[Comparative Example 1]
In the simulation reaction system 2 using the inlet HCl concentration shown in FIG. 11, the PID control method “P (proportional gain) = 10%, I = 0.1 second, D = 0.1 second, additive output lower limit 5 kg / h , “Addition amount output upper limit 100 kg / h”, the control target value (SV) of HCl treatment was set to 40 ppm and controlled. FIG. 10 shows the amount of HCl added to the bag filter and the HCl concentration at the bag filter outlet (average, 1 hour average maximum, instantaneous maximum) after treatment with fine powdered sodium bicarbonate. In addition, FIG. 12 shows the behavior of the amount of fine powdered baking soda added and the bag filter outlet HCl concentration during this control.

[Example 1]
Under the same PID setting conditions shown in Comparative Example 1, when the 6-second average of the latest HCl concentration slope is positive, the control target value (SV) is 30 ppm, and the 6-second average of the latest HCl concentration slope is negative The control target value (SV) was controlled to 40 ppm. Similarly, FIG. 10 shows the added amount of fine baking soda and the HCl concentration (average, hourly average maximum, instantaneous maximum) at the bag filter outlet after treatment with fine powdered sodium bicarbonate. Further, FIG. 13 shows the behavior of the added amount of fine powdered sodium bicarbonate and the bag filter outlet HCl concentration during this control.

  When the slope of the HCl concentration is positive (increase tendency), it can be seen that by setting the control target value low, the amount of fine powdered sodium bicarbonate added when the HCl concentration tends to increase increases, and the effect of preventing the occurrence of HCl peaks can be seen. . Further, the HCl average and the one-hour average maximum were also lowered, and the effect of stably treating HCl as intended was obtained. However, since the addition amount of fine baking soda increases compared to the conventional control (Comparative Example 1), this control is a control setting suitable for facilities that require a stable treatment with an HCl concentration of, for example, 30 ppm or less.

[Example 2]
Under the same PID setting conditions shown in Comparative Example 1, when the 6-second average of the latest HCl concentration slope is positive, the control target value (SV) is 30 ppm, and the 6-second average of the latest HCl concentration slope is negative The control target value (SV) was controlled to 50 ppm. Similarly, FIG. 10 shows the added amount of fine baking soda and the HCl concentration (average, hourly average maximum, instantaneous maximum) at the bag filter outlet after treatment with fine powdered sodium bicarbonate. Further, FIG. 14 shows the behavior of the amount of fine baking soda added and the bag filter outlet HCl concentration during this control.

  When the slope of the HCl concentration is positive (increase tendency), the effect of preventing the occurrence of the HCl peak can be obtained as in the case of Example 1, and HCl can be processed more stably than in the conventional control (Comparative Example 1). It was. Further, when the gradient of HCl concentration is negative (decreasing tendency), the control target value (SV) is increased as compared with Example 1, so that the addition amount of fine baking soda is reduced and the addition is finished, and the addition of fine baking soda is added. The amount was reduced compared to Example 1. However, since the addition amount is increased as compared with the conventional control (Comparative Example 1), this control is a control setting suitable for facilities that need to stably treat the HCl concentration at, for example, 30 ppm or less.

  Hereinafter, Comparative Example 2 and Examples 3 to 8 will be described. In Comparative Example 2 and Examples 3 to 8, control by the step control method is performed instead of the PID control method.

  Here, an outline of the step control method will be described. Unlike the PID control method, the step control method is a control method that regulates the output stepwise according to the HCl concentration at the outlet. First, in Comparative Example 2 (FIG. 15), when the HCl concentration is between the SV control target value [control output start concentration (output lower limit or higher)] and SM1, the control output is output stepwise between LO and LM1. A control output set by LM2 is output when the HCl concentration is between SM1 and SM2, and LH (control output upper limit) is output when SM2 is higher than SM2. Note that there is no output limitation in the normal PID control expression, and only LO and LH settings are set. Further, correction of the table for determining the HCl concentration and control output used in the control calculation by the HCl gradient is performed by SVA1 and SVB1, and when the HCl gradient is positive, SVA1 is subtracted from the HCl concentration used in the calculation, and when the HCl gradient is negative. SVB1 was added to the HCl concentration used in the calculation. As a result, the control output calculated when the same HCl concentration is input is the control output value when the HCl slope value is large (the acid gas concentration tends to increase), and the control output value when the HCl slope value is small. Compared to a larger format.

[Comparative Example 2]
Using the inlet HCl concentration shown in FIG. 11, the control target value (in this method, the concentration at which the control output of the alkaline agent is added to the output lower limit or more is defined as SV) in the simulation reaction system 2 is 40 ppm. Set and controlled. FIG. 10 shows the amount of HCl added to the bag filter and the HCl concentration at the bag filter outlet (average, 1 hour average maximum, instantaneous maximum) after treatment with fine powdered sodium bicarbonate. Moreover, the control output addition amount of fine baking soda according to bag filter exit HCl concentration is shown in FIG. Furthermore, FIG. 16 shows the behavior of the amount of fine powder baking soda added and the bag filter outlet HCl concentration during this control.

  In this control method, since the control output is limited by the HCl concentration range between the lower limit and the upper limit of the control output, the alkaline agent can be added step by step. From this, the excessive addition of the alkaline agent was prevented, and the addition amount of fine powdered sodium bicarbonate was greatly reduced. However, the treatment level of HCl to be treated was greatly deteriorated compared to the conventional control (Comparative Example 1).

[Example 3]
In the same step control method as in Comparative Example 2, when the 6-second average of the latest HCl concentration slope is positive, the control target value (SV) is 30 ppm, and the 6-second average of the latest HCl concentration slope is negative. The control target value (SV) was controlled to 40 ppm. Similarly, FIG. 10 shows the added amount of fine baking soda and the HCl concentration (average, hourly average maximum, instantaneous maximum) at the bag filter outlet after treatment with fine powdered sodium bicarbonate. Moreover, the control output addition amount of fine baking soda according to the bag filter exit HCl concentration is shown in FIG. Further, FIG. 18 shows the behavior of the added amount of fine baking soda and the bag filter outlet HCl concentration during this control.

  In this control method, as in Comparative Example 2, an alkali agent was added stepwise, and the effect of reducing the amount of fine powdered sodium bicarbonate added compared to the conventional control (Comparative Example 1) was obtained. Moreover, when HCl was increasing, the effect of stably treating HCl was obtained by adding fine powdered sodium bicarbonate quickly in consideration of measurement delay. This control method is a very effective method because the treatment level of HCl is improved and the additive amount reduction effect is obtained as compared with the conventional control (Comparative Example 1).

  In addition, this time, when the measured value of the HCl concentration at the bag filter was between 40 ppm and 50 ppm, the addition amount according to the HCl concentration was set and controlled, but even if this range was controlled by PID, it was between the lower limit and the upper limit of the control output. In addition, the control output is 50 kg / h or less when the HCl concentration is 50 ppm or less, and the control output is 70 kg / h or less between 50 ppm and 60 ppm, so that the same HCl treatment effect and addition amount reduction effect can be obtained. It was considered.

[Example 4]
In the same step control method as in Comparative Example 2, when the 6-second average of the latest HCl concentration slope is positive, the control target value (SV) is 30 ppm, and the 6-second average of the latest HCl concentration slope is negative. The control target value (SV) was controlled to 50 ppm. Similarly, FIG. 10 shows the added amount of fine baking soda and the HCl concentration (average, hourly average maximum, instantaneous maximum) at the bag filter outlet after treatment with fine powdered sodium bicarbonate. Moreover, the control output addition amount of the fine baking soda according to bag filter exit HCl concentration is shown in FIG. Further, FIG. 20 shows the behavior of the added amount of fine baking soda and the bag filter outlet HCl concentration during this control.

  In this control method, as in Comparative Example 2, fine powdered baking soda was added step by step and the control target value (SV) was increased compared to Example 3 when HCl was decreasing. The addition was completed, and the effect of reducing the amount added was obtained compared to the conventional control (Comparative Example 1). In addition, despite the fact that the addition amount could be reduced, the treatment level of HCl could be the same level as the conventional control (Comparative Example 1). This control method was also considered to be a very useful control method because it was able to perform the same HCl treatment as the conventional control and had the effect of reducing the addition amount.

[Examples 5 to 8]
In order to examine the appropriate average time of the latest gradient of HCl concentration for selecting the control arithmetic expression under the same control conditions as in Example 4, the gradient average time of this HCl concentration was changed and examined. Similarly, FIG. 10 shows the added amount of fine baking soda and the HCl concentration (average, hourly average maximum, instantaneous maximum) at the bag filter outlet after treatment with fine powdered sodium bicarbonate. In addition, FIGS. 21 to 24 show the behavior of the amount of fine powdered sodium bicarbonate added and the bag filter outlet HCl concentration during this control.

  As a result of this study, a large HCl peak was generated when the average time of the gradient of HCl concentration for selecting the control formula was 10 minutes (Example 8). This indicates that the timing of adding the fine powdered baking soda is deviated by increasing the average time of the inclination, and indicates that this control will fail when set to more than 7 minutes. On the other hand, when the average time was 7 minutes or less, abnormal HCl generation was not observed, and the average time of proper HCl inclination was considered to be 7 minutes or less (Examples 5 to 7).

Claims (7)

In the acid gas processing method for feedback control of the addition amount of the alkali agent based on the measurement signal of the acid gas measuring device installed in the process after adding the alkali agent to the acid gas contained in the combustion exhaust gas,
A step of at least two set a range of inclination with respect to time of the acid gas concentration,
Setting a control target value of the acid gas concentration for each of the at least two slope ranges;
Calculating a control output value indicating an addition amount of the alkaline agent based on at least the measurement signal and the control target value,
In the step of setting the control target value, the out of range of at least two slopes, the control target value to be set in a range where inclination Kiga larger of the acid gas concentration, the acid gas when the concentration of inclination outs small An acid gas processing method characterized by being smaller than a control target value set in a range of. The acid gas treatment method according to claim 1,
The method further includes the step of setting one or more new upper limit values of the control output value corresponding to the acid gas concentration between the lower limit value and the upper limit value of the control output value indicating the addition amount of the alkaline agent. A method for treating acidic gas, which is characterized. In the acidic gas processing method of Claim 1 or Claim 2,
The acid gas processing method, wherein the acid gas measuring device is a hydrogen chloride concentration measuring device by an ion electrode method. In the acid gas processing method of Claim 1 thru | or 3,
The acid gas processing method, wherein the acid gas measuring device is a sulfur oxide concentration measuring device by an infrared absorption method or an ultraviolet fluorescence method. The acid gas treatment method according to claim 1, wherein:
A method for treating acidic gas, wherein the slope of the acidic gas concentration for setting the control target value is an average value within the last 7 minutes. In the acid gas processing method according to any one of claims 1 to 5,
A method for treating an acidic gas, characterized by controlling an addition amount of an alkali agent using both a control output calculated from a hydrogen chloride concentration and a control output calculated from a sulfur oxide concentration. In the acidic gas processing method of Claim 1 thru | or 6,
The method for treating acidic gas, wherein the alkaline agent for treating acidic gas is fine powdered baking soda having an average particle diameter of 5 to 30 μm.

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