Problems existing in the disposal of Zinc Ash in Iron and Steel and the Development of "Ultimate Technology" [Zinc oxide Forum]

SMM: at the ninth Green Zinc Salt and Zinc oxide Industry Summit Forum 2021 held by SMM, Luo Tianrong, chief technical adviser of Shanxi Yusi Sheng Environmental Protection Technology Co., Ltd. And leader of the expert group of zinc salts of the Inorganic Special Committee of the Chemical Society of China, gave an in-depth explanation on "the development of the 'ultimate technology' for the disposal of zinc ash in iron and steel".

I. the important basis for the development of zinc salt industry-- the disposal of zinc ash in iron and steel.

With the rapid rise of China's iron and steel industry in the past 40 years, there are about 30 million tons of zinc ash every year, resulting in the problem of solid waste disposal of iron and steel, but at the same time, it brings opportunities for the development of zinc salt industry relying on the secondary resources of zinc solid waste. The "danger" of the metallurgical industry has become the "opportunity" of the zinc salt industry. In the past 10 years, relying on the disposal and utilization of secondary resources of zinc solid waste in the metallurgical industry-the ratio of raw materials utilization of secondary resources in the zinc salt industry has reached more than 80%, the development of China's zinc salt industry has entered a new stage.

Second, the current mainstream technology and existing problems in the disposal of zinc ash in iron and steel.

1. The technology of rotary kiln and its existing problems.

The disposal of zinc ash in iron and steel with a rotary kiln accounts for about 80% of the total zinc ash treatment, which is the current mainstream process. The advantage is that the investment is small; the existing problems are: first, it is uneconomical to dispose of less than 5% zinc ash, and only dispose of more than 5% zinc ash; second, about 40% of the iron in the ash is partially recovered in the form of iron ore after magnetic separation, resulting in a waste of iron resources; third, the use of other slag resources is extremely low-value; fourth, air pollution caused by gas emissions.

2. The technology of rotary hearth furnace and its existing problems.

Using a rotary hearth furnace to dispose of steel zinc ash is the mainstream process for steel mills to dispose of zinc ash themselves, accounting for less than 20% of the total zinc ash treatment. Existing problems:

First, large investment and high energy consumption for disposal;

Second, the failure rate of equipment operation is high;

Third, the slag iron is recovered in the form of iron pellets.

Fourth, air pollution is caused by gas emissions.

3. The development of the industry urgently needs to develop a new technology to solve the existing problems.

The two existing zinc ash disposal processes have their own problems. Under the background of the goal of "double carbon", the development of the industry urgently needs to develop a new technology of energy saving and environmental protection, so that the disposal of zinc ash can realize the "ultimate version" of resource utilization and high value under the condition of primary energy consumption.

3. New technology and its technological process:

1. The core of the new technology-- the design prototype of "coal gasification suspension smelting furnace":

Principle of suspension smelting: pulverized coal, zinc ash and pure oxygen are injected from the top of the suspension furnace, pulverized coal combustion produces high temperature and reducing gas, so that zinc ash or mineral powder is dispersed in the high temperature reduction atmosphere space of 1500-1800 ℃. In the moment of suspension falling and falling process (2-5 seconds), complete a number of melting reduction reactions of "gas + solid", "gas + liquid" and "gas + gas", so it is called "suspension smelting". It is an integrated innovation of entrained-bed coal gasification technology, suspension smelting technology, molten pool smelting technology and steam oxidation technology.

The following figure shows the specific process:

Process description:

1) pulverized coal and zinc ash, auxiliaries, pure oxygen and gas are directly injected into the furnace to produce high temperature and gas;

2) in the suspension smelting process, the zinc oxide in the zinc ash is reduced to metal zinc by carbon and carbon monoxide and gasified into zinc vapor at high temperature, and other volatiles such as potassium, sodium and chlorine are discharged together with the gas.

3) Iron and non-volatile slag are reduced into the molten pool to continue smelting, and after the slag and iron are separated, the slag is discharged as molten slag to directly produce high quality rock wool, and iron is discharged from the outlet of molten iron to directly produce high purity iron castings.

4) the zinc vapor is oxidized to zinc oxide by steam oxidation above 950 ℃, and the nanometer zinc oxide section is collected; the high temperature gas enters the waste heat utilization system to produce steam and power generation, and after the waste heat is recovered, the tail gas is washed by cold water, and the solid residue is returned to the furnace containing zinc ash.

5) recovery of potassium chloride and other salts by evaporation of washing water;

6) the gas goes into the storage tank or into the synthesis system to produce chemical products.

IV. Key points and key points of new technology development

1. Key-Technology Integration

The new technology is the integration of coal gasification, complex mineral smelting, design and manufacture of new devices, selection and adaptation of metals and refractories. More than 80% are referenced by mature examples, and nearly 20% are followed by technology. The key to a short-term breakthrough lies in the crossover, integration and cooperation of top technical personnel in different specialties, and in the engineering optimization and applicability selection of the connection between different technologies.

2. Main points-

The main contents are as follows: (1) the design and processing of high temperature melting suspension smelting furnace. This technology completes the high temperature gasification of coal, ash iron, zinc, silicon, potassium, chlorine and other minerals "gas-solid, gas-gas, gas-liquid" multiple reaction process in the main reactor. the reactor is divided into suspension smelting section and molten pool deep reduction section. at present, there is no mature industrial plant in operation, so it is necessary to carry out detailed analysis and research from the point of view of reaction thermodynamics and kinetics to determine the reactor structure and key design parameters.

(2) selection and construction of high temperature and corrosion resistant refractories for the reactor. The reaction temperature of this technology is as high as 1500-1800 ℃, and the molten slag produced by the reaction forms serious corrosion to the inner wall of the reactor, so it is difficult for conventional inorganic refractories to meet the application requirements, so it is necessary to learn from the technical achievements of high temperature reaction of coal gasification. carry out technical innovation in refractory formula and construction mode to meet the requirements of practical application.

(3) Design, material selection and processing of material burner. The feed burner, the key component of the reactor, adopts a multi-channel high temperature water cooling structure to ensure the effective mixing of materials so as to improve the efficiency of reaction, heat and mass transfer. The material selection, key structure design and operation parameters of the nozzle are deeply studied, and the material flow pattern structure of the burner is optimized.

(4) the oxidation reaction mode and engineering of zinc vapor. The oxidation of zinc vapor to zinc oxide in high temperature and high gas system is a key point in the development of new technology. The steam oxidation method and the engineering design of optimization and adaptation of the technical parameters of the new oxidation method were selected in the experiment.

(5) Safety linkage control of process system. The reaction of this technology involves pulverized coal, pure oxygen and gas, as well as reduction and oxidation. The safety and accurate control of the reaction process is the key to the safe and stable operation of the process system. It is necessary to conduct in-depth research from the aspects of process design, instrument selection, central control scheme and so on, learn from the mature technical achievements of relevant industries, optimize the process control scheme, and realize the safe, stable and efficient operation of the industrial test system.

Comparison of Zinc Ash treatment in different processes

V. the "ultimate" sign of new technology development

1. Realizing cascade clean and efficient utilization of coal under primary energy consumption.

(1) Primary utilization: coal gasification, applying the front end of entrained-bed coal gasification to produce 1500mur1800 high temperature and 80-90% gas content;

(2) secondary utilization: suspension smelting, using the high temperature and high reduction atmosphere produced by primary utilization to carry out flash smelting of smelting materials (iron ore powder, zinc ash, other minerals or solid waste);

(3) three-stage utilization: molten pool smelting, in the first stage, the ungasified carbon is used to enter the lower molten pool to further reduce and smelt the smelting materials which are not completely reduced in the second stage, and finally realize the complete utilization of carbon;

(4) four-stage utilization: zinc vapor oxidation to synthesize zinc oxide;

(5) five-stage utilization: waste heat for power generation, steam production and power generation using 950-200 heat after recovery of zinc oxide;

(6) Grade 6 utilization: gas chemical production, which is produced by using 60% of the gas content after power generation.

2. Various useful elements to realize the "final polarization" of resource utilization.

Direct production of nanometer zinc oxide from zinc resources;

Iron resources directly produce high purity iron castings;

All kinds of slag resources directly produce high quality rock wool and rock wool components;

Potassium and sodium resources directly produce potassium chloride and sodium chloride.

In terms of environmental protection, due to the use of pure oxygen combustion and carbon dioxide to transport materials, the emission of nitrogen oxides is basically zero; because all materials are reused, the discharge of solid waste is basically zero; due to the application of water circulation and treatment and utilization of each process, the discharge of wastewater is basically zero. Due to the ingenious combination of smelting and chemical production, carbon dioxide emissions are relatively reduced by more than 50%, sulfur dioxide is recovered in gas purification, and emissions are reduced by more than 90% according to national standards.