A ten-million-ton steel mill with no drainage outlet above or below ground and tens of millions of tons of wastewater per year without dripping out.
　　
Steel mill water treatment system drinks in black smelly wastewater and spits out valuable salt particles.
　　
Intelligent big data technology helps unmanned operation and makes wastewater treatment smarter.
　　
On May 19 of this year, the first domestic zero discharge project of salt crystallization wastewater built in one step by CMCSD was put into operation in Zhongtian (Nantong) Green Fine Steel Base (hereinafter referred to as Zhongtian Iron and Steel Nantong Company), truly realizing zero discharge of wastewater and no waste leaving the factory, interpreting "green water and green mountain is the silver mountain of gold" with the vivid practice of a steel plant. "It has set a green ecological benchmark for the future high-quality development of steel.

 

 

Panoramic view of Zhongtian (Nantong) green high-quality steel project
 

Going Green: Determined to pass the last kilometer of zero wastewater discharge and guard the ecological barrier from the river to the sea
　　
Zhongtian Steel Nantong, the world's largest steel base under construction, is located in Nantong, the only riverside city in Jiangsu Province. It is located in Nantong, the only riverside coastal city in Jiangsu Province, which has a unique location advantage with the intersection of national strategies such as "One Belt and One Road" construction, Yangtze River Economic Belt development and Yangtze River Delta regional integration.
　　
In November 2020, General Secretary Xi Jinping presided over a forum to comprehensively promote the development of the Yangtze River Economic Belt, emphasizing the need to strictly protect the ecological environment, comprehensively improve the efficiency of resource utilization, accelerate the promotion of green low-carbon development, and strive to build a green development demonstration belt in which people and nature coexist harmoniously. In the same year, Zhongtian Iron and Steel Nantong Company started construction, with the goal of "first-class equipment, environmental protection, brand, management and efficiency", and the clear vision of building a green steel plant benchmark.

 

 

　　Water is a necessary resource for steel production. Among all industrial fields, the steel industry consumes about 10% of water and discharges about 14% of wastewater. Achieving efficient use of water resources is an important sign of high-quality development in the steel industry.
　　
During the inspection of the water resources of the project of Zhongtian Iron and Steel Nantong Company, CMCSD engineers and technicians found that the salt content in the river water of Tonglu Canal, where the steel mill draws water, is nearly twice that of the upper reaches of Yangtze River because of its proximity to the mouth of the sea, and the steel mill is built by the sea, the salt content of its rainwater and groundwater is higher than that of inland cities. This means that the steel mill production process, whether new water or wastewater, must be desalted, otherwise the harmful substances in the salt, which are recycled in the mill for a long time, will clog or corrode the equipment, affect the product quality, and enter the nature will damage the ecology. The cutting-edge technology of "salt crystallization + zero waste water discharge" jumped into the designer's mind.
　　
The so-called "salt crystallization" is to separate the wastewater from the water and salt, pure water for steel mills to reuse, and brine through high temperature heating, evaporate the water, the remaining salt crystal, as an important raw material for some industries, the higher the purity, the more valuable to use.
　　
All along, the steel industry has been exploring the "salt crystallization" process to open the "last mile" of zero wastewater discharge, but there are not many successful cases. Zhang Xiaowei, the chief expert of water treatment technology of CMSD, analyzed that, firstly, the wastewater composition is complex and difficult to treat, and it is likely to "steam" out the hazardous waste, which poses a greater threat to the environment; secondly, the system requires extremely high design technology, and without a deep understanding of the steel mill water treatment process and the ability to control the whole situation, it may lead to the unstable operation of the facility after commissioning Stable, poor treatment effect; Third, the high cost of investment in the system, often hundreds of millions or even billions of dollars, in the severe economic situation of the market, often discourage steel enterprises.
　　
Therefore, most steel companies can only build water treatment plants to conventional filtration, part of the wastewater containing pollutants that can not be treated in depth, either used in the production of water quality requirements are not high, or discharged into rivers. Although these water quality to meet the national discharge standards, but always for the community's criticism, for the people's concern, but also the steel industry has been a pain point.
　　
"Salt crystallization" on or off? Around this issue, Zhongtian Iron and Steel and CMCSD have been discussing for several months. Shan Daming, Deputy Director of Energy Control Center of Zhongtian Iron and Steel Nantong Company, recalled, "Whether the system is successful or not 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 the customer's doubts, CMCSD, with more than 60 years of profound technical accumulation, proposed a system solution for Zhongtian Iron and Steel from top-level design to concrete implementation, and independently developed a set of water and salt balance calculation system for iron and steel enterprises, and conducted detailed research on the pollutants brought into the system in the main links of the whole plant, such as water intake, material washing, treatment and dosing, etc. Only for the water source analysis, we collected 3 river sections of Tonglu Canal Long-term water quality data from 10 monitoring points. 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 the wastewater generated from the operation of the plant-wide water system, providing a scientific basis for the design of the water system. Through split-salt crystallization, not only can the annual volume of wastewater be reduced by 12 million tons, but also 100% resource utilization of the whole plant water system can be realized.
　　
Finally, both parties agreed that CMSD, as the general contractor, and Zhongtian Iron and Steel will jointly implement the first "zero discharge" project of salt separation crystallization wastewater in the steel industry in one step, so as to guard the ecological barrier from the river to the sea and take up the social responsibility of the steel industry.

 

 

Turning green into gold: salt crystallization turns waste into treasure, "steaming" "salt grain" from black smelly wastewater to exceed the national standard
　　
In Zhongtian Iron and Steel Nantong Company, there is no drainage outlet to be found except for 4 flood outlets which are only open during the time of the great flood. Zhang Junwei, chief engineer of the water system project of Zhongye Saidi, introduced that the steel plant at the beginning of the design, insisted not to damage the ecology at the cost of both above and below ground are not set up drainage outlets, is to really do not to discharge a drop of water, not to pollute an inch of soil.
　　
So, where does the waste water go in such a large steel mill?
　　
CMSD, together with Zhongtian Iron and Steel Nantong Company, has successfully explored the economic path of "turning waste into treasure".
　　
In the central water plant located in the southeast corner of the steel mill, it receives more than 40,000 tons of wastewater from each production unit every day. The wastewater contains heavy metals, microorganisms and harmful substances such as acids, alkalis and salts, some of which are black, green and other colors, and some of which are accompanied by irritating odors. Through various purification processes, the central water plant makes pure water from the wastewater and sends it back to each production unit. The separated brine is no longer discharged to the outside world, but enters the ultra-filtration, nanofiltration and high-pressure reverse osmosis processes to obtain highly concentrated brine with mainly chloride ions, and enters the evaporation plant for the final "waste to treasure" process.

 

 

Membrane concentration workshop

 

 

Deep treatment worksho

 

 

Inside of evaporation workshop

 

 

Exterior view of evaporation workshop
 

Based on the deep treatment of conventional wastewater, CMT-Saidi designed the concentration and salt extraction technology with the core of evaporation and crystallization of nanofiltration and salt separation for the characteristics of hardness and high salt content of water source of Zhongtian Iron and Steel Nantong Company.
　　
In the evaporation workshop at the end of the central water plant, large pools and bubbling wastewater are no longer visible, but bags of white powder, i.e. sodium chloride salt, neatly stacked in a small warehouse. Workshop operator Liu Bo said, "These bags of salt are one ton in weight and can produce 20 bags per day, with a purity of more than 99%, exceeding the national standard and selling very well."

 

 

Central water plant salt storage

 

From direct discharge to zero discharge, this step in the iron and steel industry is tortuous but firm.
　　
Since 2010, CMCSD has been exploring the application of zero discharge wastewater technology in the iron and steel industry, and has built many key iron and steel enterprises' water system projects such as Xinjiang Eight Steel, Hebei Jingye, Baosteel Zhanjiang Steel and Chongqing Steel, taking the lead in realizing the transformation of zero discharge wastewater technology in domestic iron and steel industry from comprehensive introduction to independent innovation, independent design and independent integration, and through ten years' hard work with Baosteel Zhanjiang Steel Through ten years of hard work, we have promoted the metamorphosis from deep-sea discharge, near-zero discharge to zero discharge of split-salt crystallization in a step-by-step manner.
　　
In order to ensure the construction of the salt crystallization project of Zhongtian Iron and Steel Nantong Company in one step, the engineers and technicians of CMSD have made a lot of technical innovations. The central water plant has more than 20 buildings, large and small, which seem to be independent, but are actually interlinked. Any fluctuation in the water quality of one ring may affect the stability of the final salt output and the quality of the finished product.
　　
CMCSD gave full play to its general contracting service capability, combined with its leading technical advantages, integrated with domestic advanced water treatment equipment suppliers, and carried out meticulous demonstration on the setting of the whole process, including the adopted equipment, scale, functional parameters, etc., and finally tailored a water treatment plan that meets the characteristics of Zhongtian Iron & Steel Nantong. In the system commissioning stage, in the face of the "first time" to bring all kinds of unexpected difficulties, technical personnel rooted in the field, repeatedly test, calculation, and constantly optimize the configuration, and successfully complete the system commissioning, and achieve the good effect of the production of salt.
　　
Shan Daming, who is also in charge of the central water plant of Zhongtian Iron and Steel Nantong Company, said, "Since the project was put into operation, the system has been running stably and the main technical indicators have reached the industry leading level. The fact proves that Zhongtian Iron and Steel is right to choose CMCSD!"
　　
According to the introduction, the second phase of Zhongtian Iron and Steel Nantong Company will further optimize the zero-discharge project by setting up a separate sub-salt crystallization workshop for the special wastewater generated from some links to produce different types of salt products and create greater value for the enterprise.
　　
Green engine: intelligent "smart brain" for water treatment
　　
The intelligent application built by CMSD for Zhongtian Iron and Steel Nantong Company provides a new engine for more efficient, accurate and ecological management of water resources in the steel plant.

 

 

Central control room of central water plant

 

In the central control center of the central water plant of Zhongtian Iron and Steel Nantong Company, three employees are controlling the operation of the water plant by computer. On the big screen in front of them, various real-time images and data charts are presented, and with just a click of the mouse, you can view the water quality and the operation of water supply and drainage equipment of the whole plant. An operator said, in his past work in the steel plant, water supply and drainage are two sets of regulatory systems, two office locations, management is not convenient, data is not connected. Now, through centralized intelligent control, the same number of people can complete more than twice the workload in the past, and a more comprehensive understanding of the plant-wide water system, personal value has also been enhanced.
　　
Out of the intelligent control center, climb up a water treatment pond about 10 meters high, a circular pipe on the wall of the pond is spitting out a yellow-brown agent into the bubbling wastewater, the water gradually appeared a large number of suspended fine particles, that is, "alum flower". After a few minutes, the alum flower settles, and the water becomes clear as if by magic. This technology is called coagulation and sedimentation process. In the past, professionals to regularly inspect the site, based on visual observation and experience to determine the dosage of dosing, but in times of high water quality fluctuations, can not accurately calculate the amount of pharmaceuticals used, resulting in waste of pharmaceuticals, but also can not ensure stable water quality standards.
　　
In order to solve the shortcomings of the traditional process, CMCSD has independently developed the first set of alum vision intelligent dosing system in the steel industry, which uses artificial intelligence and big data technology to carry out image recognition and self-learning calculation of alum in water, and precisely control the dosing amount to ensure that the effluent water quality is 100% stable and meets the standard, and the dosing amount of pharmaceuticals is saved by 30%, and the system realizes unmanned intelligent operation. The product has been applied in several steel plants and entered the municipal field.

 

 

Intelligent and efficient sedimentation tank

 

Having "salt crystallization" to guard the last barrier of zero wastewater discharge does not mean that enterprises can rest easy. Steel mills use a lot of water to make up for the big discharge, which may also lead to the water treatment system "can't hold up" and "can't eat". At present, a 10 million tons of iron and steel enterprises need to use about 100,000 tons of water per day, equivalent to a 300,000 people in the town of 1 day of domestic water consumption. Saving at the source is also a key step in the green development of steel enterprises.
　　
It is a challenge, but also a driving force for continuous innovation.
　　
At the foot of the Zhongtian Nantong ironmaking plant, four water pipes continuously convey four types of production water treated by the central water plant, and one meter away, two other pipes send the domestic sewage and production wastewater generated in the plant back to the central water plant. Unlike in the past, each of these water pipes has a flow monitor or water quality monitor installed on it. "Such a monitor can be found in every production unit. We follow the advanced value of the industry's water quota to limit the water used in each production unit and monitor it in real time. If the water consumption exceeds the standard or the water quality does not meet the standard, it will be transmitted back to the central water plant intelligent control center and automatically alarmed." Zhang Junwei introduced.
　　
According to the calculation, after Zhongtian Iron and Steel Nantong Company is fully put into production, each ton of steel production consumes only 2.43 cubic meters of new water, which is only 1/20 of the index 40 years ago.
　　
Around Zhongtian Iron and Steel Nantong, the heavily guarded wall of the past was replaced by an encircling river, whose "river water" is actually rainwater drawn from the 7-square-kilometer plant. In order to reduce the competition with the people for water, CMT Sadie cleverly designed this 4.5 meters wide, 4.5 meters deep, 18 kilometers long plant protection river, with a storage capacity of 400,000 cubic meters, which is not only an important security facility, but also a recharge of water for the steel plant. With an investment of 500 million yuan, more than three times the cost of a conventional river construction, the plant protection river is all made of 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 more such responsible projects in the plant. For example, all the water supply and drainage pipes buried underground in the past are elevated on the ground to prevent the mutual leakage of waste water and ground water; in the key pollution areas such as raw material yard, pellet, coking, etc., the initial rainwater collection pond is set up to collect and treat the rainwater in the first 15 minutes of rain, which is the rainwater most likely to wash out pollutants, separately. In the smallest detail, Zhongtian Iron and Steel Nantong Company has effectively built a "zero emission" defense line.
　　
On the shore of Tongzhou Bay, river and sea transportation, a thousand sails are competing. Zhongtian Iron and Steel Nantong Company has created a beautiful business card of "turning green into gold" on the way of going green. CMT will also continue to adhere to the responsibility of independent innovation to lead green and low-carbon development, continuously meet the needs of harmonious coexistence between human and nature, and write more ecological answers to promote high-quality transformation and upgrading of steel.