JPH0249775B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for dry removal of acidic substances from exhaust gas containing acidic substances discharged when activated waste or sewage sludge is incinerated, or from exhaust gas from a normal industrial combustion furnace. Domestic waste or sewage sludge has traditionally been disposed of by landfilling, ocean dumping, or incineration, but these treatments have become increasingly difficult in recent years due to lack of landfill space and efforts to prevent marine pollution. . Therefore, there is now no other way to dispose of these materials other than incineration. However, if waste and sewage sludge are incinerated, SO ₂ , SO ₃ , Cl ₂ , HCl, HF and
Acidic gases such as H ₂ S are generated and pollution problems caused by these gases become a problem, so it is necessary to remove these gases. Furthermore, because fuels with high sulfur content have been forced to be used due to lack of energy sources, desulfurization treatment of exhaust gas has become increasingly necessary. Therefore, there is an urgent need to develop a method for removing acidic substances from exhaust gas that is inexpensive and easy to implement. As a result of various researches on removal agents in an attempt to remove acidic substances in exhaust gas by dry method, the present inventor added water to a mixture of cement and limestone powder and/or dolomite powder to create a hardened material, and this was used to form a hardened material. Either by crushing to a desired particle size, or by granulating a mixture of cement and limestone powder and/or dolomite powder to the desired particle size using a pan pelletizer, extruder, etc. using water as a medium, and then curing it under humidified conditions. The ivy hardened body has a large contact interface, and the constituent minerals of the hardened body are mainly CaO-SiO ₂ -H ₂ O gel, Ca
(OH) ₂ and unreacted particles, CaO―SiO ₂
- When H ₂ O gel and Ca(OH) ₂ are heated to 100-600℃, they decompose into porous amorphous material and free CaO, and the generated free CaO and amorphous material are chemically As it shows excellent activity, it has great removal performance even for acidic substances in exhaust gas at relatively low temperatures.Furthermore, acidic substance removers made by dispersing and hardening limestone powder and dolomite powder with cement are effective at high temperatures. It was found that the removal performance of acidic substances in exhaust gas is particularly high. Next, the present invention will be explained based on experimental examples. Ordinary Portland cement, silica powder (diameter 0.5mm
(below), limestone powder (diameter 0.5 mm or less), and dolomite powder (diameter 0.5 mm or less) are mixed in the proportions shown in the table below, hardened by adding water, and cured at a temperature of 20 ± 3.
C. and curing humidity (RH%) of 80% or higher for 7 days to produce a hardened cement body (40 x 40 x 160 mm).

[Table] The cured product was crushed into particles of 10 mm or less, dried at 110°C for 24 hours, and then crushed to obtain particles of 0.59 to 1.19 mm. Crushed hardened material made in this way
A fixed bed was filled with 100 g of the gas, and a desulfurization test was conducted using a gas having the following composition containing SO ₂ gas. For comparison, similar tests were conducted using limestone and dolomite, each of which had been crushed to the same particle size as the crushed material of the above-mentioned hardened material. These will be experiment numbers 5 and 6. Gas composition: SO ₂ 700ppm, O ₂ 5% CO ₂ 12%, remaining N ₂ Gas flow rate: 25/min Fixed bed cross-sectional area: 56.7cm ² Gas temperature: 600℃, 900℃ Desulfation (%) is inlet SO ₂ The results of this experiment, determined by concentration - outlet SO ₂ concentration / inlet SO ₂ concentration x 100, are shown in the attached drawing. As can be seen from the figure, the products of the present invention (experiment numbers 3 and 4) were found to have better desulfurization performance than the acidic substance remover for cement clinker cured in water, which was applied on the same day. In particular, it was observed that the desulfurization performance at 900°C was further improved. In comparison, the desulfurization rate decreases in a short time with limestone grains (experiment number 5) and dolomite grains (experiment number 6). This is thought to be because, unlike porous limestone powder and hardened dolomite powder, which are dispersed and hardened with cement, the particles are dense, so the reaction progresses only in the surface layer. In addition, it can be seen that the desulfurization rate of Experiment No. 2 using cement and silicate powder was lower than that of cement only (Experiment No. 1) at all temperatures of 600, 800, and 900°C. The present invention is based on these findings, and
Its composition is made by curing a mixture of cement and limestone powder and/or dolomite powder in the presence of water and crushing the hardened material, or by granulating the above mixture using water as a medium and hardening it. To the cured body,
It is characterized by contacting exhaust gas at 800 to 1000℃. In the present invention, as the cement, various Portland cements such as ordinary Portland cement and early strength Portland cement, or mixed cements such as blast furnace cement, silica cement, and fly ash cement are used. In addition, in order to treat exhaust gas at 800 to 1000°C, the weight ratio of cement:limestone powder and/or dolomite powder is preferably 1:1 to 1:5. The above weight ratio is 5
is not preferable because the strength of the cured product decreases rapidly when it exceeds. The limestone powder and/or dolomite powder to be used next varies depending on the method for producing the removing agent of the present invention, the composition of the gas to be treated, etc., but is generally preferably 0.5 mm or less. In particular, when granulating using an extrusion molding machine, it is preferable that the particle size is 0.1 mm or less. In addition, in the above experimental example, only the case of removing SO ₂ gas from exhaust gas was described, but SO ₃ , Cl ₂ , HCl,
Even if acidic gases such as HF and H ₂ S are contained, they can be removed in the same way as SO ₂ gas. The cured product used in the method of the present invention, that is, the acidic substance removing agent, is inexpensive, has a large removal effect, and can be used for a long period of time, so the present invention has great industrial value.

[Brief explanation of the drawing]

The drawings show the results of exhaust gas desulfurization tests at various temperatures using the acidic substance remover of the present invention, and show the relationship between desulfurization time and desulfurization rate.

Claims (1)

[Claims] 1 A hardened product obtained by curing a mixture of cement and limestone powder and/or dolomite powder in the presence of water, or a hardened product obtained by granulating the above mixture using water as a medium and hardening it. From 800 to
A method for removing acidic substances from exhaust gas, which is characterized by contacting exhaust gas at 1000°C.