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2022

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08

The first one-step zero wastewater discharge project in the steel industry was successfully implemented by MCC CCID

Author:

Tao Haiyin


There is no drainage outlet above and below the ground in a 10 million ton steel plant. Every year, tens of millions of tons of waste water do not drip out;
The water treatment system of the steel plant drinks black and smelly wastewater and spits out valuable salt particles;
Intelligent big data technology helps unmanned operation and makes wastewater treatment more intelligent.
On May 19 this year, the first domestic zero discharge project of salt separating crystallization wastewater, which was built by CCID under the general contract of MCC, was put into operation in Zhongtian (Nantong) Green Fine Steel Base (hereinafter referred to as Zhongtian Iron and Steel Nantong Company), which truly realized zero discharge of wastewater and non delivery of waste. With the vivid practice of a steel plant, it explained that "green water and green mountains are golden mountains and silver mountains", It has set a green ecological benchmark for the high-quality development of steel in the future.
Panorama of Zhongtian (Nantong) Green Fine Steel Project
Go Green: Strive to get through the last kilometer of zero wastewater discharge, and guard the ecological barrier from the river to the sea
Zhongtian Steel Nantong Company, the largest single steel base under construction in the world, is located in Nantong, the only coastal city in Jiangsu Province. It integrates the golden waterway and the golden coast, and has unique geographical advantages. The construction of the "the Belt and Road", the development of the Yangtze River Economic Belt, the regional integration of the Yangtze River Delta and other national strategies converge and overlap.
  Zhongtian Iron and Steel Nantong Co., Ltd., which started construction in the same year, has defined the vision of building a green steel plant benchmark with the goal of "first-class equipment, environmental protection, brand, management and efficiency".
Water is a necessary resource for steel production. In all industrial sectors, the steel industry accounts for about 10% of water consumption and 14% of wastewater discharge. The efficient utilization of water resources is an important symbol of the high-quality development of the steel industry.
During the investigation on the water resources of the project of Zhongtian Iron and Steel Nantong Company, the engineering technicians of MCC CCID found that the water intake of the steel plant, Tonglu Canal, was close to the sea entrance, and the salt content of the river water was nearly twice that of the upper reaches of the Yangtze River. The steel plant was built on the coast, and the salt content of rainwater and groundwater was higher than that of inland cities. This means that in the production process of the steel plant, both new water and waste water must be desalted. Otherwise, the harmful substances in the salt will block or corrode the equipment and affect the product quality if they are recycled in the plant for a long time. If they enter the nature, they will damage the ecology. The cutting-edge technology of "salt separation crystallization+zero wastewater discharge" has jumped into the minds of designers.
The so-called "salt separation crystallization" refers to the separation of water and salt from wastewater, the reuse of purified water for steel plants, the evaporation of water from brine by high temperature heating, and the remaining salt crystals, as important raw materials in some industries, are more valuable for use with higher purity.
The steel industry has always been exploring the "salt separation crystallization" process to open up the "last mile" of zero wastewater discharge, but there are few successful cases. Zhang Xiaowei, the chief expert of MCC CCID water treatment technology, analyzed that, first, the wastewater is complex in composition and difficult to treat, which is likely to "steam" hazardous waste, posing a greater threat to the environment; Second, the system has very high requirements for design technology. Without a deep understanding of the water treatment process of the steel plant and the ability to control the overall situation, it may lead to unstable operation and poor treatment effect after the facility is put into use; Third, the system investment cost is high, often hundreds of millions or even billions of yuan. Under the severe market economy situation, steel enterprises often fall short of expectations.
Therefore, most water treatment plants of iron and steel enterprises can only be built in the conventional filtering link. Some wastewater containing pollutants that cannot be deeply treated is either used in the production link with low water quality requirements or discharged into rivers. Although the water quality has met the national discharge standards, it has always been criticized by the society and worried by the people, which is also the pain point of the steel industry.
"Salt separation crystallization" or not? Centering on this issue, Zhongtian Iron and Steel and MCC CCID have conducted several months of argumentation. Shan Daming, deputy director of the energy control center of Zhongtian Iron and Steel Nantong Company, recalled: "The success of the system is a great test for Zhongtian Iron and Steel, but the first-class environmental protection is always our constant responsibility and pursuit."
In order to dispel customers' doubts, CCID, relying on more than 60 years of profound technology accumulation, has proposed a system solution from top-level design to specific implementation for Zhongtian Iron and Steel, and has independently developed a water salt balance calculation system for iron and steel enterprises. It has carried out a detailed study on the pollutants brought into the system by the main links of the whole plant, such as water intake, material washing, treatment and dosing, and only water source analysis, Long term water quality data of 10 monitoring points in 3 river sections of Tonglu Canal were collected. With more than 60 years of steel engineering experience and rich data accumulation, the system successfully predicted the key water quality and main composition parameters of wastewater generated by the operation of the plant water system, providing a scientific basis for water system design. Through salt separation crystallization, not only the annual wastewater reduction of 12 million tons can be achieved, but also 100% resource utilization of the whole plant water system can be achieved.
Finally, the two parties reached an agreement that MCC CCID, as the general contractor, and Zhongtian Iron and Steel will jointly implement the first one-step "zero discharge" project of salt separated crystallization wastewater in the steel industry, protect the ecological barrier from the river to the sea, and shoulder the social responsibility of the steel industry.
Turning green into gold: turning waste into treasure by salt crystallization, "steaming" out of black and odorous wastewater to produce "salt particles" that exceed the national first-class standard
In Nantong Company of Zhongtian Iron and Steel Co., Ltd., except for 4 flood outlets which are only open during the catastrophic flood disaster, no outlet can be found. Zhang Junwei, Chief Engineer of MCC CCID Water System Project, said that at the beginning of the design, the steel plant insisted on not damaging the ecology. No drainage outlets were set up on the ground or underground, which meant that it would not drain a drop of water or pollute an inch of land.
So, where is the waste water from the huge steel plant?
MCC CCID, together with Zhongtian Iron and Steel Nantong Company, has successfully explored the economic path of "turning waste into treasure".
The central water plant, located in the southeast corner of the steel plant, receives more than 40000 tons of wastewater from each production unit every day. These wastewater contain heavy metals, microorganisms, acid, alkali, salt and other harmful substances, some of which are black, green and other colors, and some are accompanied by irritating smell. The central water plant makes waste water into pure water and sends it back to each production unit through various purification processes. The separated brine is no longer discharged to the outside world, but immediately enters the processes of ultrafiltration, nanofiltration, high-pressure reverse osmosis, etc. to obtain highly concentrated brine mainly containing chlorine ions, and then enters the evaporation workshop for the final "waste to treasure".
Membrane concentration workshop
Advanced treatment workshop
Interior of evaporation workshop
Exterior view of evaporation workshop
On the basis of advanced treatment of conventional wastewater, CCID designed a concentration and salt extraction technology with nanofiltration salt separation evaporation crystallization as the core, aiming at the characteristics of high hardness and high salt content of the water source of Zhongtian Iron and Steel Nantong Company.
In the evaporation workshop at the end of the central water plant, there are no large pools and gurgling waste water. Instead, bags of white powder, namely sodium chloride, are stacked neatly in a small warehouse. Liu Bo, an operator of the workshop, said, "The salt weighs one ton in a bag, and can be produced into 20 bags every day. The purity of the salt reaches more than 99%, which exceeds the national first level standard and has a good market."
Salt bin of central water plant
From straight row to zero row, the steel industry has taken a tortuous and firm step.
Since 2010, MCC CCID has begun to explore the application of zero wastewater discharge technology in the iron and steel industry. It has successively built water system projects for several key iron and steel enterprises, such as Xinjiang Bagang, Hebei Jingye, Baosteel Zhanjiang Iron and Steel, Chongqing Iron and Steel, and has taken the lead in realizing the transformation of zero wastewater discharge technology in the domestic iron and steel industry from full introduction to independent innovation, independent design, and independent integration, and has worked hard with Baosteel Zhanjiang Iron and Steel for ten years, Step by step, it promoted the transformation from deep-sea emissions, near zero emissions to zero emissions of salt fractionation crystallization.
In order to ensure that the construction of salt separation crystallization project of Zhongtian Iron and Steel Nantong Co., Ltd. is in place at one step, CCID engineering technicians of MCC have made a lot of technical innovation. More than 20 buildings, large and small, in the Central Water Plant seem to be independent, but actually they are interlinked. Any fluctuation in water quality may affect the stability of final salt production and the quality of finished products.
MCC CCID gave full play to its general contracting service capability, combined with its leading technical advantages, integrated domestic advanced water treatment equipment suppliers, and conducted detailed demonstration on the whole process process settings, including the equipment, scale, functional parameters, etc., and finally customized a water treatment scheme that conforms to the characteristics of Zhongtian Iron and Steel Nantong Company. In the system commissioning stage, in the face of all kinds of unexpected difficulties caused by the "first time", technicians took root in the field, repeatedly tested and calculated, constantly optimized the configuration, successfully completed the system commissioning, and achieved the good effect of producing salt immediately after putting into production.
At present, Shan Daming, who is also the head of the Central Water Plant of Zhongtian Iron and Steel Nantong Company, said: "Since the project was put into operation, the system operation has remained stable and the main technical indicators have reached the leading level in the industry. Facts have proved that Zhongtian Iron and Steel was right to choose MCC CCID!"
It is reported that the second phase project of Zhongtian Iron and Steel Nantong Company will further optimize the zero discharge project. For the special wastewater generated in some links, separate salt crystallization workshops will be set up to produce different types of salt products, creating greater value for enterprises.
Green engine: intelligent water treatment with "smart brain"
MCC CCID's intelligent application for Zhongtian Iron and Steel Nantong provides a new engine for more efficient, more accurate and more ecological water resource management of steel plants.
Central water plant central control room
After arriving at the centralized control center of the central water plant of Zhongtian Iron and Steel Nantong Company, three employees are controlling the operation of the water plant through computers. On the big screen in front of them, a variety of real-time images and data charts are displayed. With a click of the mouse, you can view the water quality of the whole plant and the operation of water supply and drainage equipment. An operator said that in the steel plant where he used to work, water supply and drainage were two sets of supervision systems and two office locations, which made management inconvenient and data disconnected. Now, through centralized intelligent management and control, the same number of people can complete more than twice the workload in the past, and have a more comprehensive understanding of the water system of the whole plant, and their personal value has also been improved.
Out of the intelligent control center, climb up to a water treatment pool about 10 meters high. A round pipe on the wall of the pool is spitting a yellowish brown agent into the gurgling wastewater, and a large number of small suspended particles, namely "alum flowers", gradually appear in the water. After a few minutes, the alum flower precipitates, and the water becomes clear as if by magic. This technology is called coagulation sedimentation process. In the past, professionals had to go to the site regularly for inspection, and judge the dosage according to visual observation and experience. However, when the water quality fluctuated greatly, they could not accurately calculate the dosage of chemicals, resulting in waste of chemicals, and could not ensure the stable quality of water.
In order to solve the shortcomings of traditional processes, MCC CCID has independently developed the first alum visual intelligent dosing system in the steel industry. It uses artificial intelligence and big data technology to carry out image recognition and self-learning calculation for alum in water, accurately control the dosage, ensure that 100% of the effluent water quality is stable and up to standard, save 30% of the dosage, and realize unmanned intelligent operation of the system. The product has been applied in many steel plants and entered the municipal field.
Intelligent high-efficiency sedimentation tank
With the "salt crystallization" to guard the last pass of zero wastewater discharge, it does not mean that enterprises can rest easy. The water supply and discharge in the steel plant may also cause the water treatment system to be "unsustainable" and "unbearable". At present, a 10 million ton steel enterprise needs about 100000 tons of water every day, which is equivalent to the daily domestic water consumption of a town with 300000 people. Saving from the source is also a key step for the green development of iron and steel enterprises.
It is a challenge and a driving force for continuous innovation.
At the foot of Zhongtian Nantong Iron Smelting Plant, four water pipes continuously deliver four types of production water treated by the Central Water Plant. One meter away, two other pipes return the domestic sewage and production wastewater generated in the plant to the Central Water Plant. Different from the past, a flow monitor or water quality monitor is installed on each pipe. "This kind of monitor can be found in every production unit. We limit the water used in each production unit according to the advanced value of the industry's water quota, and conduct real-time monitoring. If the water consumption exceeds the standard or the water quality does not meet the standard, it will be sent back to the intelligent control center of the central water plant and automatically alarm," Zhang Junwei said.
According to calculation, after the full production of Zhongtian Iron and Steel Nantong Company, only 2.43 cubic meters of new water will be consumed for each ton of steel produced, which is only 1/20 of that 40 years ago.
Around Zhongtian Iron and Steel Nantong Company, the previously heavily guarded wall was replaced by a surrounding factory protecting river, whose "river" is actually rain water drawn from the 7 square kilometers of factory area. In order to reduce competition with people for water, CCID of MCC ingeniously designed this factory protecting river which is 4.5 meters wide, 4.5 meters deep and 18 kilometers long, with a storage capacity of 400000 cubic meters. It is not only an important security facility, but also a water supply for steel plants. The investment in the Huchang River is 500 million yuan, more than three times the cost of conventional river construction. It is poured with reinforced concrete, which can eliminate internal and external leakage and prevent ecological damage caused by rainwater that may be mixed with harmful substances.
There are many such responsible projects in the factory. For example, the water supply and drainage pipes buried underground in the past are all overhead on the ground to prevent the mutual leakage of wastewater and groundwater; In the key pollution areas such as raw material yard, pelletizing, coking, etc., a primary rain collection tank is set up to collect and treat the 15 minute rain in the early rain, that is, the rain most likely to wash out pollutants. See the real chapter in the details, and Zhongtian Iron and Steel Nantong Company has effectively built a "zero emission" defense line.
By the Tongzhou Bay, river sea combined transportation and thousands of sails are launched. Zhongtian Iron and Steel Nantong Company has created a bright business card of "turning green into gold" on the way of pursuing green. MCC CCID will also continue to adhere to the responsibility of leading green and low-carbon development through independent innovation, constantly meet the needs of harmonious coexistence between people and nature, and write more ecological answers to promote high-quality transformation and upgrading of steel.