JPS58227A - Dry type exhaust gas desulfurizing method - Google Patents

Abstract

PURPOSE:To obtain easily an adsorber having high mechanical strength and packing density, by classifying carbonized coals by the difference of specific gravity and using carbonized coals having a heavy specific gravity as an adsorber and using carbonized coals having a light specific gravity as a reducing agent. CONSTITUTION: Fuel coals 1 are crushed and classified by a crusher 109 and a classifier 110 and are fed partially to a carbonization furnace 111. Carbonized coals 24 are classified by a specific gravity difference classifier 112 to which sea water or the like is charged, and carbonized coals having a light specific gravity which are floated up are dried by a drier 113 and are fed to a reducing tower 104 and are used as a reducing agent 14. Precipitated carbonized coals having a heavy specific gravity are dried and activated by a drying furnace 114 and an activating furnace 115 and are fed as an adsorber 12 to an adsorbing tower 101. Thus, since the adsorber 12 classified by the specific gravity difference has no expanded grains and has high hardness and packing density, the adsorber and the reducing agent suitable for a use are selected from fuel coals easily.

Description

Detailed Description of the Invention The present invention is a dry flue gas desulfurization method that removes sulfur oxides from fuel exhaust gas by producing adsorbents and reducing agents from coal, and recovers sulfur oxides as elemental sulfur. Regarding the law.

Conventionally, various methods for removing sulfur oxides from combustion exhaust gas have been proposed and improved. Among these desulfurization methods, a typical desulfurization method is a method in which sulfur oxides are absorbed into an alkaline solution such as limestone and then recovered as gypsum through oxidation treatment, etc., as shown in 1. Limestone-gypsum method.

However, in the "limestone-gypsum method", the amount of gypsum discharged from large equipment such as thermal power plants is enormous, and storage and transportation of this gypsum becomes a problem, as well as drainage and
There is a water problem. Therefore, a dry flue gas desulfurization method that can recover elemental sulfur as a by-product, which is lighter than gypsum, has been attracting attention.

In the dry flue gas desulfurization method, sulfur oxides in the combustion exhaust gas are adsorbed onto an adsorbent, and the adsorbent that has adsorbed the sulfur oxides is regenerated by thermal desorption and recycled. In addition, the desorption gas generated by thermal desorption has a high concentration of sulfur dioxide (SO,
), the desorption gas reacts with carbon and is partially recovered as sulfur, and the by-product H2S gas is further reduced to elemental sulfur under a catalyst. Therefore, in such a dry flue gas desulfurization method, the adsorbent is recycled and regenerated in an adsorption tower and a desorption tower, so mechanical wear occurs during the circulation process, and sulfur oxides are adsorbed by the adsorbent as dilute sulfuric acid. As a result, the adsorbent is thermally desorbed and regenerated. That is, since the adsorbent is consumed by mechanical wear and chemical wear, it is necessary to constantly replenish an amount of adsorbent corresponding to the consumed amount. Therefore, it has been desired to replenish adsorbents that are less likely to be worn out during the desulfurization process using a simple method.

The inventors have already proposed that the adsorbent used in the flue gas desulfurization process be produced from thermal coal used as fuel for coal-fired power plants. However, when producing an adsorbent from thermal coal, the adsorption performance is affected by the type of fuel coal, and furthermore, when the thermal coal is carbonized, slightly coking coal is mixed in, so the coal expands and when carbonized. There was a problem that the adsorbent produced had weak mechanical strength and reduced packing density.

The object of the present invention is to produce an adsorbent with high mechanical strength and packing density from thermal coal, and at the same time to produce a reducing agent used in the reduction process of SO2 gas, which can be used in the flue gas desulfurization process. The objective is to prevent damage to the adsorbent and to easily replenish the adsorbent and reducing agent.

That is, fuel coal is a mixture of various types of coal, which is crushed into appropriate particle sizes and carbonized. Carbonization is 700-850
Do it at about 0. At this time, the slightly caking coal partially expands and devolatilizes while increasing its volume, while the non-caking coal devolatilizes with almost no change in volume and completes carbonization. Here, by classifying the carbonized coal by specific gravity difference, particles with a change in volume (expanded particles) are separated from particles with no change in volume (mainly non-caking coal). Next, particles with no volume change have high mechanical strength and high packing density, so they are activated and used as an adsorbent in the flue gas desulfurization process, and particles with a volume change are used to convert high concentration SO into elemental sulfur. It is used as a reducing agent.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

Coal 1 is combined with powdered coal supplied from streams 2, 3, and 4.5 and burned in coal-fired boiler 100.

Combustion gas 6 is combined with process exhaust gas in stream 7 and adsorption tower 1
01. In the adsorption tower 101, sulfur oxides in the combustion gas are adsorbed by an adsorbent (carbonized coal), and the clean exhaust gas 8 is released into the weather after undergoing processes such as dust removal. The adsorbent adsorbing sulfur oxides is transferred from stream 9 to desorption tower 1.
02, and is regenerated as an adsorbent by thermal desorption. The regenerated adsorbent 10 is then passed through the classifier 10
3, where the mechanically depleted adsorbent is removed and then fed from stream 4 to the coal boiler 100.

The regenerated adsorbent 11 is combined with the adsorbent 12 sent from the adsorbent manufacturing process and is supplied to the adsorption tower 101.

The adsorbent will thus circulate through streams 9, 10.11.

The gas containing high concentration S02 desorbed in the desorption tower 102 is
Stream 13 sends the SO2 reduction column 104Vc, where it reacts with carbon, and the SO□ in the gas is mainly partially S
, H, and S. Carbon (carbonized coal) used in the reduction tower 104 is supplied from stream 14, and carbonized coal consisting of ash and some residual carbon is extracted from stream 15 after reduction treatment of SO and gas. It is desirable that the extracted carbonized coal be treated in a boiler (not shown) or the like.

reduction! The reactant gas discharged from 104 and containing sulfur vapor from stream 16 is cooled in a sulfur condenser 105 where the sulfur vapor in the reactant gas is condensed and a portion of the sulfur in the reactant gas is recovered from stream 17. .

In sulfur condenser 105, the remaining sulfur vapor-containing gas is introduced from stream 18 into Claus reactor 106.

In the Claus reactor 106, hydrogen sulfide (H2S) generated by the reduction reaction of SO, residual s02, and oxygen (02) undergo the following reaction (1) in the presence of a Claus catalyst.
, (2) by 80. and produces elemental sulfur (S).

2H2S+SOz→2H20+38 --Song/Song (2)
The reaction gas discharged from Claus reactor 106 and containing sulfur vapor is sent from stream 19 to sulfur condenser 1O27 where the sulfur vapor in the reaction gas is condensed and recovered from stream 20. Since the gas discharged from the sulfur condenser 107 may contain toxic gases, this gas is introduced via stream 21 into the oxidation column 108 where it is oxidized.
The oxidizing gas is combined with the flue gas 6 from the stream 7 and then introduced into the adsorption column 101 .

A method for producing and replenishing an adsorbent and a reducing agent in such a dry flue gas desulfurization process will be described.

The fuel coal 1 of a coal-fired power plant is transferred from a stream 22 to a crusher 10
9, where it is crushed into appropriate particle sizes.

If raw coal is classified directly outside the system, the following crushing,
No classification operation is required. The crushed coal 22 is then classified into appropriate particle sizes in a classifier 110, and is transferred from a stream 23 to a carbonization furnace 1.
Sent to 11. Most preferably, the pulverized coal in the classifier 110 is combined with the fuel coal 1 from stream 2 and combusted in the coal-fired boiler 100.

In the carbonization furnace 111, the temperature is slowly raised to about 700r to 850C, and the carbonization coal is sent from the stream 24 to the specific gravity difference classifier 112.

Water, seawater, or oil is appropriately selected and injected into the specific gravity difference classifier 112, and when carbonized coal at room temperature is introduced, particles that have changed in volume (carbonized coal with a small specific gravity) float to the surface. However, particles that do not change in volume (carbonized coal with high specific gravity) settle. The carbonized coal having a low specific gravity obtained by the specific gravity differential classification in the specific gravity differential classifier 112 is dried in the dryer 113, and then sent from the stream 14 to the reducing column 104 and used as a reducing agent.

The carbonized coal having a high specific gravity obtained by the specific gravity differential classification in the specific gravity differential classifier 112 is dried in the dryer 114 and then sent to the activation furnace 115, where it is activated by reacting with the steam of the stream 28, and becomes an adsorbent. 12 and sent to the adsorption tower 101. In addition, in the specific gravity difference classifier 112, when oil such as heavy oil is used as the liquid for specific gravity difference classification, a film of lint remains on the surface of the carbonized coal that has been subjected to specific gravity difference classification.

Therefore, it is desirable to introduce the carbonized coal that has been subjected to specific gravity differential classification and second drying to a pyrolysis furnace (not shown) to decompose the oil remaining on the surface of the carbonized coal. The reactant gas in the activation furnace 115 is withdrawn from stream 29 and is recovered as a heat source in the process in the same manner as the carbonization gas.

In this way, the adsorbent 12 is replenished to the adsorption tower as the sum of the adsorbent waste extracted from stream 4 and the chemical damage consumed in the desorption tower 102.

Here, we conducted an experiment using Australian coal A as fuel coal.
The effects of the present invention were confirmed.

When A fuel coal was pulverized and its average caking properties were examined, the Button index was 1.5. Fuel coal A was heated to 700C at a heating rate of 1.5 to 2C/m in a rotary kiln furnace, maintained at this temperature for 1 hour, and then cooled to room temperature in a N2 gas atmosphere to produce carbonized coal.

Here, when carbonized coal was put into 14.2 tons of water,
The ratio of sediment to floating matter was 53% for sediment and 47% for floating matter. The micro-strength hardness and packing density of the sediments and floats obtained here are compared with 4 as follows. Microstrength hardness of sediment is 82%
On the other hand, the amount of floating matter was low at 58%, and the packing density was 380 g/l, which was smaller than the packing density of 680 g/l. Further, by changing the specific gravity, the classification ratio of sediments/floating substances can be adjusted, and this ratio of sediments/floating substances is adjusted by the required amount of adsorbent and reducing agent as described above.

The adsorbent obtained by activating settled carbonized carbon has no expanded particles and has high hardness and packing density.

On the other hand, the expanded carbonized carbon is used as a carbon source in the contact reaction between SO and carbon.

In this catalytic reaction, there are no restrictions on the hardness or packing density of the carbon particles, so expanded carbonized carbon is sufficient.

In the present invention, since the reducing agent and the adsorbent can be selected by gravity classification, the coal used as the raw material is not limited to one type of coal, but may be a mixture of several types of coal. Furthermore, in the above embodiment,
The means of differential gravity classification utilizes the floating and settling of carbonized return powder in a liquid, but when water, seawater, etc. is used as this liquid, a large amount of heat is required to carbonize the carbonized return powder after differential gravity classification. Become. In order to avoid such problems of wet specific gravity differential classification, dry specific gravity classification is desirable.

The dry specific gravity differential classification method can employ, for example, a method in which carbonized coal is sieved into several particle size range groups and then the carbonized coal in each particle size range group is separately supplied to an air classifier.

The wind classifier may be either a horizontal flow type or a vertical flow type.

As described above, according to the present invention, carbonized coal is classified by specific gravity,
The carbonized carbon with a heavy specific gravity is used as an adsorbent, and the carbonized carbon with a light specific gravity is used as a reducing agent, so an adsorbent with high hardness and packing density can be obtained, and the carbonized carbon with a light specific gravity is used as a reducing agent. Since the adsorbent and reducing agent can be used as a replenisher, adsorbents and reducing agents can be supplied according to the characteristics of each adsorbent and reducing agent. In addition, adsorption tower-
When the adsorbent is regenerated and circulated between desorption towers, the mechanical wear and tear associated with the circulation can be reduced, which has the effect of reducing the running costs associated with dry flue gas desulfurization. Moreover, since the packing density becomes large, there is an effect that the capacity of the adsorption tower for unit combustion exhaust gas processing amount can be reduced.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of the present invention. 100...Coal-fired boiler, 101...Adsorption tower, 1
02...Desorption tower, 103...Classifier, 104...
SO7 reduction tower, 105... Marrow condenser, 106...
Claus reaction tower, 107...Sulfur condenser, 108...
・Oxidation tower, 109... crusher, 110... classifier,
111... Carbonization furnace, 112... Specific gravity differential classifier, 11
3,114...Dryer, continued from page 1 of 115 ■Applicant Babcock Hitachi Co., Ltd. 2-6-2 Otemachi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. In a dry flue gas desulfurization method that includes a step of adsorbing sulfur oxides in the exhaust gas to an adsorbent, and a step of bringing the desorption gas into contact with a reducing agent to convert the sulfur oxides in the desorption gas into elemental sulfur, The specific gravity value to be sorted is selected according to the amount of adsorbent and reducing agent required in the adsorption process and the reduction process, and the carbonized coal powder is classified based on the specific gravity difference, and the carbonized coal powder with a large specific gravity is classified. A dry flue gas desulfurization method characterized in that charcoal is activated and then used as the adsorbent, and carbonized carbon having a low specific gravity is used as the reducing agent.