JPS58193721A - Treatment of waste gas of coal fired boiler - Google Patents

Abstract

PURPOSE:To decrease the amt. of waste water to be treated of a wet desulfurizer in the stage of subjecting the waste gas of a coal fired boiler to treatments of denitration, air preheating, dust collection at low temp. and wet desulfurization by adding an alkali slurry thereto between the desulfurizer and the air preheater. CONSTITUTION:Ammonia is added through a supply pipe 2 to the waste gas of a coal fired boiler 1 and NOx is converted to nitrogen and water in a denitrator 3. The waste gas is then introduced into a spray dryer 4 where a Ca or Mg alkali slurry is supplied to the gas through a supply pipe 5 to adsorb and remove the sulfur trioxide, hydrogen chloride and hydrogen fluoride in the waste gas. The waste gas is further recovered of heat in an air preheater 6, is removed of fine powder together with coal ash in a dust collector 7 and is recovered of heat in a heat exchanger 8, whereafter the waste gas is introduced into a wet desulfurizer 9 and is adsorbed away of sulfur dioxide. The cleaned waste gas is released through a chimney 10 into the atmosphere.

Description

[Detailed Description of the Invention] The present invention denitrates coal-fired boiler exhaust gas with high dust and nitrogen content.
By using air preheating, low-temperature dust collection, and wet desulfurization, the concentration of ammonium compounds contained in the ash collected by the dust collection device is reduced, and chlorine and fluorine ions are removed from the circulating water of the wet desulfurization device. The present invention relates to a method for treating coal-fired boiler exhaust gas that can prevent the accumulation of water and reduce the amount of wastewater.

The exhaust gas from the right-leg firing boiler is introduced in a highly dusty state to an ammonia catalytic reduction type denitrification device for denitrification, then the exhaust gas is introduced to an air preheater for heat recovery, and then the exhaust gas is sent to a low-temperature electrostatic precipitator. When the exhaust gas is introduced into a dust collector such as a wet desulfurizer to remove dust, and the exhaust gas is further introduced into a wet desulfurization device for desulfurization treatment, the exhaust gas to which ammonia has been added is led to the denitrification device filled with a denitrification catalyst. , +V40□→L + 3/2 H,0 According to the reaction equation, nitrogen oxides are converted to harmless nitrogen and water, and at the same time, the denitrification catalyst is converted to SO, and in order to increase the oxidation ability, the following equation is used: The reaction also progresses.

so, -1-1/20t→SO.

Therefore, the exhaust gas from the denitration equipment contains SO3 along with unreacted leak ammonia, and NH4H3 due to the reaction between this leak ammonia and SO3 in the exhaust gas.
Ammonium compounds such as O, -(NH,), SO, etc. contained in the coal ash collected by the dust collector give off an ammonia odor.

Due to the elution of ammonia into the water system, adverse effects are expected when dumping and using coal ash. In order to avoid this effect, reduction of leak ammonia from the denitrification equipment is of course being considered, but at present only insufficient results have been obtained. In addition, a method of heating the coal ash collected by a dust collector containing ammonium compounds to thermally decompose the ammonium compounds and remove ammonia from the coal ash is also being considered, but thermal decomposition of ammonium compounds requires a considerable high temperature. However, since a large amount of heat source is required, there is a problem that the processing cost becomes high.

On the other hand, since hydrogen chloride gas and hydrogen fluoride gas contained in the exhaust gas of a coal-fired boiler are absorbed and removed together with sulfur oxides in a wet desulfurization device, chlorine ions and fluoride ions are accumulated in the circulating water. Chloride ions - When fluorine ions accumulate excessively.

It is necessary to blow out a part of the circulating water to prevent corrosion of the equipment or a decrease in the sulfur oxide removal rate, which has the drawback of increasing the amount of wastewater to be treated.

As a result of intensive research to solve the above problems, the inventors of the present invention found that the exhaust gas temperature downstream of the denitrification device was 250 to 50.
Ca, Mg-based alkaline slurry in the 0°C range! J-woF
It was discovered that A-Ca-Mg-based alkaline slurry absorbs sulfur trioxide, hydrogen chloride, and hydrogen fluoride in the exhaust gas, and at the same time dries into a fine powder due to the high temperature atmosphere, making it economical. This led to the invention of a technically superior method for treating coal-fired boiler exhaust gas.

That is, the present invention introduces coal-fired boiler exhaust gas in a highly dusty state into an ammonia catalytic reduction type denitrification device for denitrification, then introduces the exhaust gas into an air preheater to recover heat, and then passes the exhaust gas to a low-temperature dust collector. In this method, Ca-Mg-based alkaline slurry is introduced into the high-temperature exhaust gas between the denitration equipment and the air preheater. By adding sulfur trioxide, hydrogen chloride, and hydrogen fluoride in the flue gas and absorbing and removing them, the content of ammonium compounds in the coal ash collected by the dust removal equipment is partially reduced, and the content of ammonium compounds in the circulating water of the wet desulfurization equipment is further reduced. It is an object of the present invention to provide a method for treating coal-fired boiler exhaust gas that can prevent the accumulation of chlorine ions and fluorine ions and reduce the amount of wastewater to be treated.

Hereinafter, the tree invention structure will be explained based on the drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the invention. After ammonia is added to the exhaust gas discharged from the coal-fired boiler 1 from the ammonia supply pipe 2, it is led to the denitrification device 6 filled with a denitrification catalyst, where nitrogen oxides are converted into harmless nitrogen and water. . At step b, the exhaust gas is introduced into the spray dryer device 4. A Ca-Mg based alkali slurry supply pipe 5 is connected to this spray dryer device 4.

For example, an aqueous slurry of fine calcium hydroxide powder and/or fine calcium oxide powder is supplied. Note that when calcium oxide fine powder and water are mixed to form a slurry, most of the calcium monoxide is converted to calcium hydroxide, so it is simply referred to as calcium hydroxide slurry.

In the spray dryer 4, sulfur trioxide and hydrogen chloride-hydrogen fluoride in the exhaust gas are absorbed and removed by reacting with the added calcium hydroxide slurry as shown in the reaction formula below.

Ca(OH), -1-8o, -+Ca5O, +H,
0Ca(OH)! + 2 HC1→Ca C1x +
2Hx 0Ca(OH), +2HP→CaF, +2H2
0 At the same time as the above reaction, the slurry is dried and becomes a fine powder because of the high temperature atmosphere of 250 to 500°C. The spray dryer 4 may be any device that has a structure that allows exhaust gas and slurry to be sufficiently mixed and has a residence time of one gas of 0.5 to 5 seconds, preferably 1 to 3 seconds, and is generally used. It can also be used. The exhaust gas exiting the spray dryer device 4 is heat-recovered in the air preheater B, and then led to the dust collector 7, where the fine powder is removed together with the coal ash in the exhaust gas. As the dust collector 7, an electrostatic precipitator, a bag filter, etc. are used.

After the dust-removed exhaust gas is heat-recovered in a gas-to-gas heat exchanger 8, it is led to a wet desulfurization device 9.

Sulfur dioxide in the exhaust gas is absorbed and removed. The exhaust gas purified in step b is released into the atmosphere from the chimney 10.

Next, Examples and Comparative Examples will be explained.

Example 1? SO using an experimental device consisting of a 7-monia contact 11-element denitrification device and a spray dryer device.

) An ICI-HF removal experiment was conducted. The sample gas is coal-fired boiler economizer outlet gas, approximately -NOx: 30
0ppm-SOx: 1,500ppm-”*:3
%-Co, : 12%-H, O: 1[]]%-N, : Remaining amount of soot and dust: 20F/Nm''.

The experiment was conducted under the conditions shown in Table 1, and the results were as shown in FIG.

Table 1 Exhaust gas amount (Nm”/Hr) 500 Nubre dryer population temperature (“C) 380
Spray dryer outlet temperature ("C) 360
~370 Spray Dryer Population Sos Concentration (ppm)
30-40 sprays per dryer population HCI concentration (
PPIll) 40-5050 Spray dryer HP concentration (ppm) 8-10 Injection Ca (OH
), amount (f/Hr) 50-7 DO Example 2 Part of the test was carried out using experimental equipment consisting of an ammonia catalytic reduction type denitrification device, a scrubber: dryer device, an air preheater, and a dust collector (electrostatic precipitator). An experiment was conducted to confirm the reduction in the concentration of ammonium compounds in the ash collected by the dust device. The same sample gas as in Example 1 was used. Table 2 shows the experimental conditions.

Table 2 Exhaust gas amount (Nrn”/Hr)
500 spray - dryer population temperature ("C)
380 spray - dryer outlet temperature ('C)
370 Air preheater outlet temperature ('C)
150 Dust collector outlet temperature ('C)
140 spray - dryer population so, concentration (ppm
) 30 Souffle dryer population HCI concentration (ppm) 40 □ Nublade dryer population IF concentration (ppm) 10 Spray dryer population NH, concentration (ppm) 5
Injection Ca (OH), amount (y/Hr) 500 experiment results,
So at the spray dryer outlet, 9 degrees - HCI concentration,
HF concentration-NH, concentration is less than lppm-20p, respectively
pm, 1 ppl! l-5ppm, so, concentration, HCI concentration, HF concentration-NH at the exit of the dust collector.

? 1 degree breakout 1 ppm or less, 20 PPm-I
PPm was -5 ppm. Furthermore, the NH,- concentration in the coal ash collected by the dust collector was less than 9/20, indicating that the coal ash contained almost no ammonium compounds.

Comparative Example Using the same equipment as Example 2, Ca(OR), slurry 13-
The experiment was conducted under the same conditions as in Example 2 except that no injection was performed. As a result of the experiment, the SO at the spray dryer outlet
, concentration, HCI concentration - HF concentration - NH, concentration is 3 oppm - 40 PPm, IQ ppm, 5 ppm, respectively.

SO, concentration, HCI concentration - HF concentration at the exit of the dust collector.

NH, concentration is less than IPPm, 40ppm-
It was 10 ppm-1 ppm or less. Further, the NHJ concentration in the coal ash collected by the dust collector was about 200~/kq, and a large amount of ammonium compounds were contained in one coal ash.

[Brief explanation of drawings]

Fig. 1 is a systematic explanatory diagram showing an example of an apparatus for carrying out the method of the present invention, and Fig. 2 shows the results of an example of the present invention. It is a graph showing the relationship between HCI and IF removal rate. 1. Coal-fired boiler, 2. Ammonia supply pipe, 6.
Denitration equipment, 4... Spray dryer equipment, 5... Ca
-Mg-based alkali slurry supply pipe, 6... air preheater,
7... Dust collector -8... Gas/gas heat exchanger, 9
・・Wet desulfurization equipment, 10・Chimney

Claims (1)

[Claims] 1 Coal-fired boiler exhaust gas is introduced in a highly dusty state into an ammonia catalytic reduction type denitrification device for denitrification, then the exhaust gas is introduced into an air preheater to recover heat, and then the exhaust gas is introduced into a low-temperature dust collector. In the method of desulfurization by introducing the exhaust gas into a wet desulfurization equipment including dust removal, ca-M8 is added to the high temperature exhaust gas between the denitrification equipment and the air preheater.
A method for treating coal-fired boiler exhaust gas, which comprises adding an alkaline slurry to absorb and remove sulfur trioxide, hydrogen chloride, and hydrogen fluoride in the exhaust gas.