Heating furnace flue gas fixed bed dry desulfurization

Steel rolling heating furnaces are divided into regenerative heating furnaces and conventional heating furnaces according to different combustion methods;

Using air and gas dual regenerative combustion technology, the exhaust gas temperature is usually ~150℃; Using air preheating technology, the exhaust gas temperature is usually ~300℃;

In order to better and sustainable development of the ecological environment, China's national standard and many provincial and municipal landmarks have agreed on the flue gas emission index of heating furnaces, and the trend of environmental protection is becoming more and more severe;

Therefore, it is imperative to desulfurize the flue gas of the heating furnace;

Based on nearly 20 years of experience in general contracting of heating furnace projects and in-depth understanding of the heating furnace's own process, combined with the comprehensive application and practice of various desulfurization forms, Shanghai Xuanding is closely combined by the Industrial Furnace Division and the Environmental Protection Division. Formed a relatively complete desulfurization technology and process route, and implemented in many projects, and achieved very ideal results;

1. Selection of sulfide treatment plan

1.1 Basic description of various process forms There are usually three ways for flue gas sulfide treatment:

method one:

The soot and air smoke from the original heating furnace are introduced into their respective reaction towers, and the ultrafine particles of sodium bicarbonate are injected into the reaction towers. Sodium carbonate, and generate carbon dioxide and water. The highly active sodium carbonate fully contacts with the acidic components such as SO2 and SO3 in the flue gas of the heating furnace and chemically reacts to realize the solidification and removal of SO2.

The by-products from the desulfurization system enter the subsequent respective bag filters along with the flue gas.

The dust collected by the bag filter can be collected by the centralized ash bin, and the specific method depends on the actual layout of the site.

Mill Preparation System

reaction tower

dust collector

Method two:

This technology is a fixed bed (or intermittent moving bed) dry desulfurization technology, which uses a desulfurizer to catalyze the oxidation of sulfur dioxide in the flue gas to sulfur trioxide, which is then absorbed by calcium hydroxide to generate calcium sulfate:

SO2 + 1/2 O2 → SO3

SO3 + Ca(OH)2 → CaSO4 + H2O

Adopting fixed-bed technology (or intermittent moving bed), alkali (can be lime, sodium carbonate, magnesium hydroxide, etc.) and shaped particles of catalyst are installed in the desulfurization reactor. After the flue gas flows, the sulfur dioxide in it is oxidized into Sulfur trioxide reacts and solidifies into calcium sulfate (gypsum) solids.

As shown in the figure below, it is mainly composed of several towers with a circular structure, which are compactly arranged;

For large flue gas volume or limited site space, square towers can also be used;

Method three:

The sodium-calcium double-alkali desulfurization process (NaOH/Ca(OH)2) is a process developed on the basis of the limestone/gypsum method combined with the sodium-alkali method;

As long as it is a gas-liquid reaction, it can be classified as a wet method, and the specific forms can be limestone gypsum method spray absorption, soda-calcium method, double alkali method, etc. The basic principle is the comprehensive application of spraying, demisting and other methods;

Because the wet method is prone to the following problems:

Particulate matter problem: Desulfurization is a gas-liquid contact reaction sprayed by atomizing nozzles, and particles are easily entrained in the process, resulting in excessive particulate matter at the outlet. At present, in order to meet the export dust emission index, the general wet desulfurization tower will add a wet electric mist eliminator in the follow-up to meet the export requirements. Dust indicators are stable.

Temperature drop and white plume problems The humidification and cooling of flue gas produces white plumes. At present, most projects add whitening facilities and increase investment according to environmental protection requirements.

Corrosion problems of pipelines and equipment There are many operating equipment, high failure rate, strong system corrosion, and short equipment life; frequent system maintenance, calcium sulfate and magnesium sulfate generated by this process are easy to block in the dead corners of the tower, nozzles or pipelines, causing outage of the entire system.

The water consumption is huge, and the solid waste and liquid waste are difficult to deal with

Based on the above-mentioned problems, the wet method was adopted by many enterprises a long time ago, and subsequently dismantled, and now it is rarely used;

1.2 Specific comparison instructions

Note 1: Judging from the situation of multiple production projects, the inability of the desulfurizer quality to be effective and stable is a pain point for many customers; based on this, Shanghai Xuanding, as an engineering contractor, has its own desulfurizer material production base; at the same time, it provides maintenance service, responsible for the final emission index, and provide one-stop services such as desulfurizer supply, replacement, waste recycling and treatment;

2. Application and effect of fixed bed desulfurization technology

2.1 Basic principle and process layout

This technology is a fixed bed dry desulfurization technology, which uses a desulfurizer to catalyze the oxidation of sulfur dioxide in the flue gas to sulfur trioxide, which is then absorbed by calcium hydroxide to generate calcium sulfate:

SO2 + 1/2 O2 → SO3

SO3 + Ca(OH)2 → CaSO4 + H2O

The realization of this method in engineering is to adopt a fixed-bed technology. The formed particles of alkali (can be lime, sodium carbonate, magnesium hydroxide, etc.) and catalyst are installed in the desulfurization reactor. After the flue gas flows, the sulfur dioxide in it is oxidized. It becomes sulfur trioxide and is solidified by reaction into calcium sulfate (gypsum) solid.

The whole process does not use water and does not generate waste water. The operation control process is simple and easy to control.

The desulfurization tower adopts a unitized design in structure, which can adapt to the load changes of the heating furnace through flexible unit opening and closing, and the system layout is flexible and can be operated under positive and negative pressure.

The air smoke and soot flue gas are drawn from the flue and collected into the desulfurization device system respectively, and the up-to-standard flue gas from the desulfurization device system is pressurized and discharged to the chimney through the induced draft fan.

Air and smoke process: Heating furnace flue gas outlet - original induced draft fan - desulfurization tower - (booster fan) - original (new) chimney. Soot process: Heating furnace flue gas outlet - original induced draft fan - desulfurization tower - (new fan) - original (new) chimney.

2.2 Comparison of various schemes of fixed bed technology

The development of fixed bed desulfurization technology so far is mainly divided into the following forms:

According to the airflow direction, it is divided into axial flow and radial flow;

The axial flow air flows from bottom to top, and the desulfurizer runs from top to bottom, and the two are in relative circulation;

The radial flow air enters from the side, and the desulfurizer runs from top to bottom;

The height of the radial flow desulfurization tower is about 25 meters or more, and such a high cross-section will inevitably cause airflow deviation;

The self-weight of the desulfurizer will cause serious pulverization of the bottom, resulting in aggravated bias flow;

After the desulfurizer sinks under its own weight, a vacuum is formed in the upper part, causing short circuit and bias current;

The failure direction of the desulfurizer is the left and right directions, and the discharge is the lower part first, so the desulfurizer cannot be fully utilized, resulting in an increase in operating costs;

Therefore, we choose the axial flow method; according to the number of towers, it is divided into single tower form and multi tower form;

The single-tower form is that the desulfurization tower is a whole tower, and the inlet and outlet are a gas collecting box. Even if there is an independent desulfurization tower unit inside, the inlet air cannot be adjusted in units, and the problem of bias flow is serious;

The multi-tower form is that multiple desulfurization towers are relatively independent, and each tower has its own air flow adjustment valve, which can easily and flexibly adjust the air intake of each tower, so as to achieve uniform and controllable air flow; therefore, we choose the multi-tower method;

2.3 Technical Features and Advantages of Shanghai Xuanding

Key points of desulfurization tower

——Distribution uniformity The design of the distribution cone enables the desulfurizer to be self-adapted to the bottom cone section (air distribution cone) for accumulation during the charging process, the thickness of the material layer is uniform, and the air flow is not biased from the desulfurizer itself;

——Air distribution uniformity (anti-bias flow design) The air distribution cone is in the form of a stainless steel porous plate. The final porosity is determined according to the flow field simulation and resistance calculation on the orifice plate, and there are multiple oblong holes; the size of the hole should be the same as that of the desulfurizer. Corresponding physical size, will not cause blockage;

Targeted desulfurizers Desulfurizers use calcium hydroxide as the base material and are covered with active ingredients. When manufacturing desulfurizers, the actual sulfide concentration on site should be combined to make the strength and activity/efficiency of desulfurizers reach the best balance point. Desulfurizer production The process includes dry mixing, wet mixing, extrusion molding, drying (including foaming) and other processes;

Dry mixing and wet mixing should ensure uniform mixing;

The extrusion process should pay attention to the extrusion pressure control, so as to control the strength of the product to meet the needs of the working conditions of the project;

After drying, it should be ensured that the material has no free water to ensure efficiency;

The final product should be used after the simulated flue gas performance test, etc.;

Introduction of Shanghai Xuanding Desulfurizer/Environmental Material Production Base In order to better solve several problems existing in the actual production of the owner:

1) Due to various emergencies or emergencies, a large amount of desulfurizer materials are urgently needed in a short period of time;

2) The desulfurizer is a solid waste, and it is cumbersome to treat and recycle it harmlessly;

3) Environmental emission indicators are required to be adjusted frequently, and professional personnel are required to maintain the operation of the environmental protection system and to meet the emission standards. Therefore, some companies outsource the operation and maintenance of the environmental protection system to ensure that the indicators always meet the emission standards;

In response to the above, Shanghai Xuanding has established a material factory with the production of desulfurizers, denitration agents and corresponding new product research and development as its main business content, and has laid out a number of desulfurizer production bases according to different regions;

Designed to address:

1) Using Xuanding's own formula, from OEM processing to own factory production, can better ensure material performance, quality, construction period;

2) When the customer is in urgent need, the entire factory can be dedicated to produce materials for the customer to solve the customer's urgency;

3) For enterprises that have requirements for harmless treatment and solid waste recycling, they can fully respond, and it is more convenient to have their own factories to conduct solid waste recycling;

4) Especially for customers with operation and maintenance needs, it can provide the most comprehensive service and the most timely response;

2.4 Production effect and indicators

Shanghai Xuanding has successively built fixed-bed desulfurization projects such as Tangshan Guoyi, Shandong Juneng, Shanxi Xinghua, Anhui Xuanli, etc.; Xuanding's own PRTL series desulfurization towers are adopted, and the axial countercurrent/uniform distribution structure is adopted. The desulfurization agent of its own factory can achieve very ideal desulfurization and dust reduction effects;

Shanghai Xuanding Metallurgical Technology Group Co., Ltd.

Jointly prepared by Environmental Protection Division + Industrial Furnace Division