PAFP flue gas desulfurization technology and engineering application

PAFP flue gas desulfurization technology and engineering application

PAFP flue gas desulfurization technology is an activated carbon adsorption desulfurization technology developed with the goal of reducing sulfur dioxide emissions, purifying the atmospheric environment, and recovering sulfur resources. The adsorption catalytic ability of activated carbon is used to absorb sulfur dioxide in the flue gas and make sulfuric acid, which recovers valuable sulfur resources while eliminating sulfur dioxide pollution. At present, the process technology for directly producing ammonium phosphate composite fertilizer by using desulfurized dilute acid and the process technology for producing ferrous sulfate have been successfully developed. In theory, many sulfate products can be produced by using desulfurized acid, so the technology has broad and flexible practicality. Different from the traditional flue gas desulfurization method, the technology does not need to add desulfurization absorbent at any time, and has no desulfurization raw material on-site preparation and transportation, no desulfurization waste residue, and no secondary pollution. In 1998, an industrial test device with a flue gas volume of 10×104 Nm3/h was built in the Douba Power Plant. The main technical performance indicators are: desulfurization rate: ≥85%, sulfuric acid concentration: ≥30% I. Overview

(1) PAFP flue gas desulfurization process technology development process

The Phosphate Ammoniate FerTIlizer Process (hereinafter referred to as PAFP) flue gas desulfurization technology is a new process technology developed by China itself. Up to now, all technical preparations for construction demonstration equipment and engineering applications have been completed. This technology was listed as a national key scientific and technological project during the “Seventh Five-Year Plan” period. It completed the intermediate test of flue gas desulfurization of power plants with a capacity of 5000 Nm3/h. In 1991, it passed the appraisal and acceptance of national organizations. The project is listed as a key industrial pilot project in Sichuan Province. An industrial test device with a treatment capacity of 10×104 Nm3/h was built in Sichuan Damba Power Plant. In July 1998, it passed the technical appraisal hosted by the Sichuan Science and Technology Commission. The National Development Planning Commission and the Ministry of Science and Technology have included the PAFP flue gas desulfurization technology in the 1999 “Guidelines for Priority Development of High-tech Industrialization Key Areas” to gradually achieve the goal of complete set and large-scale.

(II) Process principle of PAFP flue gas desulfurization

The ammonium phosphate fertilizer method (PAFP) flue gas desulfurization technology is a mechanism that utilizes activated carbon to catalyze the oxidation of acid to remove the SO2 from the flue gas to form H2SO4. Through the comprehensive utilization process, the ammonium phosphate composite can be finally produced. Comprehensive utilization products such as fertilizer or ferrous sulfate. PAFP flue gas desulfurization technology is a combination of flue gas desulfurization and comprehensive utilization of desulfurization by-products. The process principle is that SO2 in the flue gas is adsorbed when passing through the activated carbon, and SO2 adsorbed on the surface of the activated carbon is catalytically oxidized to SO3, which is in contact with H2O in the flue gas, adsorbed in the activated carbon in the form of sulfuric acid, and is carried out after the activated carbon is saturated. The washing is regenerated and finally produced as a product of dilute sulfuric acid. This technology has a uniquely enhanced process for the selection and washing of activated carbon, so that the recovered SO2 can produce dilute sulfuric acid with a concentration of about 30%.

The reaction mechanism of desulfurization of activated carbon to acid can be expressed by the following formula:

In the PAFP flue gas desulfurization technology, the comprehensive utilization of desulfurization by-products is a recycling process that can be developed according to local conditions to produce sulfate series products. At present, ammonium phosphate compound fertilizer with a grade of ≥35% (N+P2O5) is developed. Process, and production of ferrous sulfate (FeSO47H2O) product process with a purity of more than 96%. In the industrial test, the desulfurization by-product is ferrous sulfate, that is, the liquid slag discharged from the power plant boiler is enriched with iron particles, and the iron slag is selected and desulfurized by-produced dilute sulfuric acid is metered into a special reaction tank. The reaction is heated, and the reaction product is concentrated, cooled, crystallized, and separated to obtain a ferrous sulfate (FeSO4·7H2O) product having a purity of 94% or more. In addition, the use of dilute sulfuric acid and iron as raw materials has recently produced iron-red products with higher added value.

The comprehensive utilization of desulfurization by-products in PAFP flue gas desulfurization technology is a recycling process that can be developed according to local conditions to produce sulfate series products. In the future, it can also be directly concentrated into dilute acid to produce acid, so that PAFP desulfurization technology can complete the flue gas. In the process of desulfurization, the removed sulfur is used as a resource to obtain environmental benefits and direct economic benefits through comprehensive utilization.

Second, the technological advancement and comparison of technical indicators of similar products

(1) Advancement of PAFP technology

The development of PAFP flue gas desulfurization technology is mainly to solve the problem of sulfur dioxide pollution in large and medium-sized coal-fired boilers. PAFP flue gas desulfurization technology not only solves SO2 pollution to protect the atmospheric environment, but also recovers sulfur resources and comprehensively utilizes them, which makes it superior to traditional flue gas desulfurization technology in engineering investment, operating cost and technological advancement. Its characteristics are as follows:

1. Activated carbon adsorption oxidative desulfurization technology, no need to add limestone, lime and ammonia desulfurization absorbent at any time, on-site preparation and transportation without desulfurizer raw materials, no desulfurization waste residue, no secondary pollution. Operation management is easy and quick to start.

2. Developed special activated carbon for desulfurization, the active groups such as phenolic hydroxyl group and hydrazine-type carbonyl group naturally exist on the surface can increase the oxygen molecule transfer rate, and its adsorption catalytic oxidation process has greater adsorption capacity than conventional activated carbon. The active group on the surface of the activated carbon is not modified by supplementing additives such as iodine and ammonia, and has no problem of loss, so it has a long-term catalytic oxidation effect. The desulfurization activated carbon catalyst of the PAFP device can be used for one-time use for more than four years.

3. The research and development step-by-step advancement of the enhanced washing and regenerating technology can improve the acid production concentration under the premise of ensuring the desulfurization efficiency, so that the PAFP technology has a higher desulfurization rate and a higher acid production concentration. Tests show that the PAFP technology can stabilize the desulfurization rate at ≥85% when the acid production concentration is >30%. When the acid concentration is required to be low (<15%), the desulfurization rate can reach over 95%.

4. Developed the comprehensive utilization technology of dilute sulfuric acid, so that the sulfuric acid produced after desulfurization can be directly used to produce by-products, and the sulfur resources can be effectively recycled while removing SO2. Its desulfurization by-products can make flue gas desulfurization have certain economic benefits.

5. Adsorption catalytic reaction desulfurization tower is the key equipment for PAFP flue gas desulfurization. It integrates dust removal and desulfurization, and can be applied to desulfurization of high dust, high temperature and large flow flue gas. The desulfurization tower enables the activated carbon desulfurization system to work continuously and reliably when the dust content of the flue gas is >400 mg/m3. Under the condition of ensuring higher desulfurization efficiency, dilute sulfuric acid with a concentration of ≥30% can be obtained.

(II) Comparison of main technical performance indicators with technical indicators of similar products at home and abroad

PAFP technology is an activated carbon desulfurization technology developed for coal-fired power plant flue gas, which can eliminate sulfur dioxide pollution and recover sulfur resources. In the past, the concentration of sulfuric acid produced by activated carbon desulfurization technology at home and abroad was too low, generally only 5 to 15%. For such dilute acid, only concentrated or added lime to form gypsum can not be directly used, thus affecting the technology. Development, and PAFP flue gas desulfurization technology can increase the desulfurization concentration to about 30%, which provides the possibility of direct utilization of desulfurized dilute acid. At the same time, PAFP desulfurization technology can adapt to high dust content (~400mg/m3) and a wide range of SO2 concentration (500～3500ppm). See Table 1 for comparison between PAFP desulfurization technology and foreign Hitachi and German Lurgi Technologies using activated carbon desulfurization to acid.

Table 1 Comparison of PAFP Desulfurization Technology and Foreign Activated Carbon Desulfurization Acid Production Technology

Third, the scope of application and market prospects

(1) Scope of application of PAFP flue gas desulfurization technology

PAFP flue gas desulfurization technology has a wide range of applications. For coal-fired power plant flue gas, industrial coal-fired boiler flue gas, smelter, chemical plant and other SO2-containing tail gas, PAFP desulfurization technology can be used. This technology has certain requirements for the dust content and SO2 concentration and gas volume of the flue gas. The general dust-containing flue gas needs to be reduced to 400mg/Nm3 by the dust collector to enter the desulfurization system. The concentration of SO2 in the flue gas should not be higher than 4000 ppm. The amount of flue gas treated should generally be above 10×104Nm3/h.

(II) Market prospects of PAFP flue gas desulfurization technology

China is the world's largest coal producer and consumer. Coal accounts for 73% of total energy and is one of the few countries in the world that uses coal as its main source of energy. As China's energy is mainly coal-burning and some areas use high-sulfur coal, coal-fired equipment failed to take desulfurization measures, resulting in increasing sulfur dioxide emissions, causing serious environmental pollution. The emission of coal-fired flue gas S02 is the main factor for the development of acid rain pollution. The loss of acid rain in the country exceeded 110 billion yuan in 1998, equivalent to 5,000 yuan per ton of S02, which has become an important factor restricting China's economic and social sustainable development. factor.

China is a country with a large population, a large agricultural country, and a large fertilizer country. In 2005, the demand for phosphate fertilizer was 10 million tons. Sulfuric acid is the main raw material for the production of phosphate fertilizer. At present, the annual output of sulfuric acid in China exceeds 23 million tons, equivalent to 15 million tons of S02. In recent years, due to the relative lack of sulfur resources in China, a large amount of sulfur has been imported to meet the demand for phosphate fertilizer growth. It is estimated that the total annual import of sulfur in China will exceed 2.5 million tons, equivalent to S02 5 million tons, accounting for 1 billion yuan of foreign exchange. In addition, the annual import of phosphate fertilizer is 5 million tons, equivalent to 6 million tons of imported sulfuric acid, equivalent to S02 4 million tons. Therefore, according to this development trend, by 2005, China's imported sulfur resources will be more than 10 million tons. Together with the domestically produced S02, the S02 required by China's fertilizer industry will exceed 20 million tons per year. On the one hand, the emission is more than 20 million tons/year, which is wasted, and it also causes a huge loss of acid rain of more than 110 billion yuan. On the other hand, it requires 20 million tons/year, and it also costs a large amount of foreign exchange to introduce. Therefore, while controlling the sulfur dioxide emissions to protect the atmospheric environment, the effective recovery of sulfur dioxide in the flue gas is utilized as a sulfur resource, which is beneficial to profit and turn waste into treasure. It is the development direction of flue gas desulfurization technology development research suitable for China's national conditions.

PAFP is an activated carbon desulfurization technology developed for coal-fired flue gas. It utilizes the adsorption catalytic ability of activated carbon to absorb sulfur dioxide in flue gas and make it into sulfuric acid. It recovers valuable sulfur resources while eliminating sulfur dioxide pollution. Since this technology is similar to or even slightly lower in the investment and traditional abandonment method, and its comprehensive utilization in the operation process is available as a by-product, it will benefit economically in addition to solving environmental pollution, which is more than the traditional abandonment method. Obvious competitiveness. Power plants in the southwest, south China and other areas burning high-sulfur coal have good prospects for popularization and application.

Fourth, industrial application examples

(1) Basic conditions of the project

The project was built in the bean dam power plant owned by Yibin Power Generation Plant in Yibin County, Sichuan Province. The Douba Power Plant has two 50MW generator sets and two 100MW generator sets with a total installed capacity of 300MW. The unit is equipped with two 230t/h coal-fired boilers and two 410t/h coal-fired boilers. The desulfurization project treats part of the flue gas of the 4# boiler of the plant, which is about 10x104Nm3/h, which is equivalent to the flue gas volume of the 120t/h boiler, which corresponds to the 25MW generator set.

The coal used in the Douba Power Plant is mainly anthracite from the Furong Coal Mine in Yibin, and also supplies coal from some small coal mines. The coal quality analysis is shown in the following table:

Table 2 Coal quality analysis data

CY	HY	NY	OY	SY	WY	AY	VY	QY
60.55	2.38	0.94	1.44	3.74	6.50	24.45	13.28	5511
51.46	2.12	0.66	1.27	3.27	9.50	31.52	9.33	4570
48.90	2.24	0.91	1.35	3.50	9.00	34.10	9.00	4500
56.38	2.38	0.70	1.72	4.35	9.06	34.47	9.06	5053

It can be seen from the coal quality analysis data that the sulphur content of the coal-fired power of the Bean Power Plant is usually 3-4%, which is a high-sulfur coal. When the boiler is in normal combustion, the concentration of SO2 in the flue gas can reach 3000ppm or more.

Two 410t/h coal-fired boilers are equipped with an electrostatic precipitator. The dust collector is three electric fields. When working normally, the dust content of the dust at the outlet of the dust collector is about 200mg/Nm3. However, due to the abnormal operation of the precipitator, the dust content of the exhaust gas of the electrostatic precipitator is usually around 400mg/Nm3.

The by-product dilute sulfuric acid produced by desulfurization is partly used to produce ferrous sulfate and partly used to neutralize the pH of the ash water in power plants. The ferrous sulfate produced is sold directly, and some are further processed into iron red for sale. The iron granules, which are the raw materials for the production of ferrous sulfate, are all selected from the slag pool of the liquid slagging of power plant boilers, and do not need to be purchased.

(II) Main design parameters of the project

Flue gas inlet parameters of the desulfurization unit:

Sulfur dioxide concentration 2000～4000ppm

Dust concentration ≤400mg/Nm3

Flue gas temperature 100～150°C

Flue gas flow rate 70000～140000Nm3/h

Desulfurization equipment operating parameters:

Handling of flue gas: ~100000Nm3/h

Desulfurization rate 80% to 90%

Single tower operation cycle 40 hours

Annual running time 600 hours

Annual desulfurization amount 4,380 tons / year

Annual production of acid capacity of 22,350 tons / year (30% H2SO4)

Technical parameters of ferrous sulfate production:

Annual output of 1,000 tons / year

Annual consumption of sulfuric acid (30%) 1,250 tons / year

Annual iron particle consumption (including Fe85%) 240 tons / year

Reaction temperature 80 ° C

Crystallization temperature 20 ° C

Product ferrous sulfate purity ≥95%

(iii) Major equipment and structures

The main equipment of the project is activated carbon desulfurization tower, and the desulfurization tower is four. T

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