JP2883365B2 - Control device for wet flue gas desulfurization unit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for controlling a sulfuric acid flow rate of a wet flue gas desulfurization device, and particularly suitable for reducing the amount of sulfuric acid and recovering gypsum with a stable purity. The present invention relates to a novel wet flue gas desulfurization device.

[Related Art] In recent years, as the demand for power generation increases, the size of boilers using fossil fuels as main fuels has also increased, and the degree of influence of power generation boilers on air pollution has been increasing.

The emission regulations of sulfur oxides (SO _x ), which account for a large proportion of the pollutants that increase this air pollution, tend to be stricter year by year. Under this circumstance, since the second oil shock, Japan's power industry, which has been using oil as its main fuel, is switching to lime, which is cheaper and has a more stable supply.

In addition, this lime is imported from a very large number of countries and production areas for the purpose of long-term stable supply and easing trade imbalances, and several tens of types of lime are used in one power plant. There are examples. Due to the difference in the properties of this coal,
Not only the combustion characteristics in the boiler differ, but also the desulfurization characteristics vary greatly depending on the properties of the combustion exhaust gas in the boiler.

In addition, as the boiler becomes larger, the boiler must be started and stopped on a daily and weekly basis (Daily Star
t Stop, Weekly Start Stop, hereinafter simply referred to as DSS, WSS)
Driving is repeated.

As a characteristic of recent power demand, the difference between the maximum and minimum power loads has increased with the increase in nuclear power generation, and there has been a tendency to shift the boiler for thermal power generation from base load to load adjustment. By changing the pressure of the boiler in accordance with the load to perform the variable pressure operation, the so-called supercritical pressure region for full load and the subcritical pressure region for partial load, the power generation efficiency at partial load is improved. number%
This is because it can be improved.

However, since the DSS operation is frequently performed on a daily basis and the WSS operation is performed on a weekly basis, the amount of exhaust gas and the gas properties greatly differ depending on the load change.

With the increase in coal type used in the boiler and the increase in operational changes and speeding up, the flue gas desulfurization unit that treats boiler exhaust gas also follows changes in the operating state of the boiler, and in each operating state A need has arisen for optimal operation with minimal utility.

Hereinafter, the problems of the related art will be specifically described with reference to the drawings.

For example, wet flue gas desulfurization equipment installed in thermal power plants, etc., uses calcium carbonate (CaCO ₃ ), calcium hydroxide [Ca
(OH) ₂ ] or calcium oxide (CaO) is used to absorb sulfur oxides (SO _x ) in exhaust gas from boilers and the like, and oxidize the resulting calcium sulfite. The most common method is to recover calcium sulfate, that is, gypsum.

FIG. 3 shows a schematic configuration of a conventional wet flue gas desulfurization apparatus using this limestone or lime.

In FIG. 3, the untreated gas 2 at the inlet of the absorption tower 1 is introduced into the absorption tower 1 and comes into gas-liquid contact with the calcium-based absorption liquid slurry in the absorption tower 1 to obtain sulfur contained in the untreated gas 2. Oxides, dust, HCl and HF are removed. After the entrained mist is removed by the demister 3, the purified processing gas is discharged to the atmosphere as the processing gas 4. On the other hand, the required amount of the absorbent slurry is supplied to the absorption tower circulation tank 6 of the absorption tower 1 through the absorption slurry pipe 5, and the absorption liquid slurry is sent to the top of the absorption tower 1 by the circulation pump 7, and is subjected to sulfur oxidation. Absorb things.

The absorption slurry which has absorbed the sulfur oxides and becomes calcium sulfite in the absorption tower 1 returns to the absorption tower circulation tank 6, but since the air 8 is supplied into the absorption tower circulation tank 6, Most of calcium sulfite becomes gypsum. A part of the circulating absorbent slurry is extracted to the relay tank 10 by the extraction pipe 9. The sulfuric acid stored in the sulfuric acid tank 22 is pressurized in the relay tank 10 by the pump 23 and added via the conduit 26 to convert unreacted limestone and the like into the gypsum 17 to collect high-purity gypsum 17. The slurry in the relay tank 10 is withdrawn through a slurry pump 12 and a conduit 13 to a mixer 14 and concentrated to a predetermined concentration. After that, the gypsum 17 is dewatered by a separator 15 and collected by a conveyor 16 as a solid. On the other hand, the supernatant water (water) of SIKKNA 14 is
After 18, it is stored in the water tank 19.

Part of the excess water is discharged from a blow water conduit 21 to a waste water treatment device (not shown) through a blow water control valve 20 in order to keep the concentration of impurities such as chlorine ions in the system at a certain value or less. The remaining superfluous water is returned to an absorption liquid slurry tank (not shown) or the like and reused in the system.

In the above system, when the concentration of dust and sulfur oxide in the gas flowing into the desulfurizer changes, the composition of the absorption slurry in the absorption tower 1 also changes, and finally the purity of the gypsum also changes. Will do. That is, since the by-product gypsum contains dust and unreacted limestone as impurities, the gypsum purity increases as the sulfur oxide concentration increases and the dust concentration decreases. Also, the lower the unreacted limestone concentration, the higher the gypsum purity.

On the other hand, by-product gypsum is taken up by a cement maker or a board maker and used as an additive for cement or a material for a gypsum board, so that its purity is regulated. Therefore, as described above, sulfuric acid is added in the relay tank 10 in order to convert unreacted limestone into gypsum.

The pH in the relay tank 10 is measured by a pH meter 25.

[Problems to be Solved by the Invention] However, in the above prior art, the method of controlling the amount of sulfuric acid supplied to the relay tank 10 is basically provided in the extraction pipe 9 from the absorption tower 1 as shown in FIG. The control was performed in proportion to the amount of the extracted slurry measured by the flow meter 27. That is, this control is performed on the assumption that the composition in the extracted slurry is substantially constant, and the relationship between the sulfur oxide concentration and the dust concentration is not considered at all. For example, under conditions where the sulfur oxide concentration is high and the dust concentration is low, wasteful sulfuric acid is supplied even when a sufficiently high gypsum purity can be maintained without converting unreacted limestone to gypsum.

As described above, in the above-described conventional technology, the influence on the gypsum purity due to the change in the exhaust gas properties and the operating conditions has not been considered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device which controls the purity of gypsum during operation and supplies a minimum necessary amount of sulfuric acid by comparison with a reference value.

[Means for Solving the Problems] The above object of the present invention is achieved by the following constitutions.

That is, in a wet flue gas desulfurization device that absorbs sulfur oxides in the combustion exhaust gas of a boiler or the like with an absorbent slurry such as limestone and collects gypsum as a by-product, the flow rate of the exhaust gas flowing into the desulfurization device, Sulfur oxide concentration, sulfur oxide concentration in exhaust gas at the desulfurization unit outlet, dust concentration, absorbent slurry flow rate supplied to the absorption tower of the desulfurization unit, absorption slurry flow rate extracted from the absorption tower, and limestone in the absorption slurry as gypsum Measuring means for measuring the sulfuric acid flow rate to be supplied and the oxidation rate of oxidizing calcium sulfite to gypsum, and calculating the purity of by-product gypsum based on the measurement value of each measuring means, calculating the purity of by-product gypsum A required sulfuric acid amount calculating means for calculating a required sulfuric acid amount that satisfies a predetermined purity reference value of by-product gypsum, and supplies the calculated required sulfuric acid amount to the absorption slurry. A main amount of sulfuric acid supply means, the control apparatus for wet type exhaust gas desulfurization system provided with.

[Action] The gypsum purity in the absorption slurry is determined from the ratio of the total amount of the gypsum produced in the supply tower and the amount of gypsum converted by sulfuric acid in the unreacted limestone to the total solid weight in the absorption slurry.

Next, the amount of sulfuric acid added is determined so that the calculated value of the gypsum purity becomes as equal as possible to the reference gypsum purity. If the gypsum purity exceeds the reference value, the sulfuric acid flow rate is decreased, and if the gypsum purity is opposite, the sulfuric acid flow rate is increased.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a control system diagram according to the present invention, and FIG. 2 is a schematic configuration diagram of a wet flue gas desulfurization device according to an embodiment of the present invention.

In FIGS. 1 and 2, the members denoted by reference numerals 1 to 27
This is the same member as the member shown in the figure.

In FIG. 2, an exhaust gas flow meter 31,
Sulfur oxide concentration meter in exhaust gas 32, dust concentration meter in exhaust gas
33 are provided, and at the outlet of the absorption tower 1, a sulfur oxide concentration meter 34 in the exhaust gas is provided.
35, an absorbent slurry flow meter 36 is provided in the absorbent slurry pipe 5. As shown in the control system diagram of FIG. 1, a limestone extraction slurry flow meter 27, an absorption tower extraction slurry flow signal 37, an exhaust gas flow meter 31, an exhaust gas flow signal 38 at the absorption tower entrance, and a sulfur oxide concentration meter 32 indicate an absorption tower. Sulfur oxide concentration signal 39 at the inlet, dust concentration signal 40 at the absorption tower inlet from the dust concentration meter 33, sulfur oxide concentration signal 41 at the absorption tower outlet from the sulfur oxide concentration meter 34, absorbent slurry from the absorbent slurry flow meter 36 Flow signal 42 and sulfuric acid flow meter
From 35, each signal of the sulfuric acid flow rate signal 43 is output to the calculator 44. Then, the gypsum purity is calculated in the gypsum purity calculator 44 based on each of the signals. The required sulfuric acid amount is calculated in a required sulfuric acid amount calculator 47 based on the calculation result 45 and a preset purity reference value 46, and based on the calculation result 48, a controller is used.
The sulfuric acid supply flow rate control valve 24 is controlled via 49.

In FIG. 1, the process amount detection signals 37 to 43 are
The gypsum purity is calculated by inputting the values to the following.

 Gypsum purity is expressed by the following equation.

x ₀ : gypsum purity (%) A: amount of gypsum produced in the absorption tower (kg / h) A = amount of absorbed sulfur oxides (kg mol / h) x (oxidation rate) x 172 B: not oxidized in the absorption tower Amount of calcium sulfite (kg / h) B = Absorbed sulfur oxide amount × (1-oxidation rate) × 129 C: Gypsum amount of unreacted limestone converted by sulfuric acid (kg / h) C = Sulfuric acid supply amount ( kg mol / h) × 172 D: Amount of limestone not converted by sulfuric acid in unreacted limestone (kg / h) D = [Amount of limestone supplied (kg mol / h) −Amount of sulfur oxide absorbed (kg mol / h)] × 100−C × 100/172 E: The amount of dust collected in the absorption tower E = Amount of gas at the entrance of the absorption tower × Dust concentration Here, the oxidation rate is obtained by manual analysis according to the equation (2).
Input to the calculator as a constant.

[CaSO ₃ ]: CaSO ₃ concentration in slurry (mmol / h) [CaSO ₄ ]: CaSO ₄ concentration in slurry (mmol / h) The above-mentioned oxidation rate is periodically checked by manual analysis.

The actual operating conditions of the absorption tower 1 are constantly changing,
Since a large amount of the absorption liquid slurry is held in the absorption tower circulation tank 6, the change in the liquid properties is delayed. Therefore, the calculation of the gypsum purity in the absorption liquid slurry takes into account the volume effect (time delay) due to the amount of liquid retained in the absorption tower circulation tank 6 with respect to the above equation (1).

When the gypsum purity can be continuously calculated in this way, the required sulfuric acid flow rate can be calculated by comparison with the reference purity 46. F = amount of supplied limestone (kg mol / h) −absorbed sulfur oxide (kg m
ol / h) and substituting this into equation (1) gives Is obtained. Next, in formula (1), the required sulfuric acid flow rate (C × 98/17) corresponding to the minimum value of C that satisfies the following condition:
2) We will ask for 48.

Gypsum purity calculated value 45 ≧ reference purity 46 ……………………………………………………………… (4)
Control is performed by 49, and the control valve 24 is operated.

In the equation (1), A depends on the sulfur oxide concentration in the exhaust gas, D depends on the operating conditions, and E depends on the dust concentration in the exhaust gas. B is a value that can be almost ignored during normal operation. That is, according to the present invention, the operation satisfying the standard value of the gypsum purity can be performed by adjusting C in consideration of A, D, and E which change depending on the exhaust gas condition and the operating condition.

[Effects of the Invention] According to the present invention, the sulfuric acid flow rate can be controlled to a minimum according to changes in operating conditions such as diversification of the properties of coal as a boiler fuel and intermediate load operation.

By considering the relationship between the sulfur oxide concentration and the dust concentration, etc., for example, under conditions where the sulfur oxide concentration is high and the dust concentration is low, a sufficiently high gypsum purity can be maintained without converting unreacted limestone to gypsum. In this case, there is no need to supply unnecessary sulfuric acid.

[Brief description of the drawings]

1 is a control system diagram according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a wet flue gas desulfurization apparatus according to an embodiment of the present invention, and FIG. 3 is a schematic configuration diagram of a conventional wet flue gas desulfurization. FIG. 4 is a conventional sulfuric acid flow control system diagram. 1 ... absorption tower, 6 ... absorption tower circulation tank, 10 ... relay tank,
22 ... sulfuric acid tank

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Okawa 6-9 Takaracho, Kure-shi, Hiroshima Pref. Inside the Kure Factory, Bukucock Corporation (72) Inventor Masakatsu Nishimura 6-9 Takaracho, Kure-shi, Hiroshima Pref. Inside the Kure Factory Co., Ltd. (72) Inventor Shigeru Nozawa 6-9 Takara-cho, Kure City, Hiroshima Prefecture Inside the Babcock Hitachi Kure Factory Co., Ltd. (56) References JP-A-63-294927 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B01D 53 / 34,53 / 50

Claims (1)

(57) [Claims] 1. A wet flue gas desulfurization apparatus for absorbing sulfur oxides in combustion exhaust gas from a boiler or the like with an absorbent slurry such as limestone and recovering gypsum as a by-product, the flow rate of the exhaust gas flowing into the desulfurization apparatus and the exhaust gas Sulfur oxide concentration in exhaust gas, sulfur oxide concentration in exhaust gas at the desulfurization unit outlet, dust concentration, absorbent slurry flow rate supplied to the absorption tower of the desulfurization unit, absorption slurry flow extracted from the absorption tower, limestone in the absorption slurry Measuring means for measuring the flow rate of sulfuric acid supplied to make gypsum and an oxidation rate for oxidizing calcium sulfite to gypsum, and calculating the purity of by-product gypsum based on the measurement values of each measuring means, A required sulfuric acid amount calculating means for calculating a required sulfuric acid amount that satisfies a predetermined purity reference value of by-product gypsum based on the purity of the gypsum; and supplying the calculated required sulfuric acid amount to the absorption slurry. Controller of the wet flue gas desulfurization apparatus is characterized by providing necessary and the amount of sulfuric acid supply means.