Chapter Twenty-Nine: The Blast Furnace (Technical Article)

The blast furnace was the most difficult part of the entire project. To build it, a special team was formed to collect all the technical information on its structure, materials, and construction methods. A 125-cubic-meter blast furnace, over ten meters high, and weighing several thousand tons, was the largest industrial equipment the Senators had ever handled. Its difficulty surpassed all previous industrial construction projects.

Structurally, a blast furnace must meet two prerequisites: the furnace charge must be able to descend uniformly, and the furnace gas must be able to rise uniformly across all horizontal sections.

In a modern blast furnace, the uppermost part is the throat, where the furnace charge is loaded by a special charging machine. To protect the throat from being damaged by the impact of the charge, a layer of steel bricks is inlaid on it. The charge is added to the throat and is immediately dried and preheated by the hot furnace gas rising from below. The furnace gas is then discharged through a pipe at the top of the furnace. This part must be very tightly sealed to prevent the leakage or return of the gas, which is mostly carbon monoxide, from poisoning the workers.

Part of the discharged furnace gas is reintroduced into the blast furnace as fuel, while another part is sent to the hot blast stove to heat the blast.

The furnace body is a cone, smaller at the top and larger at the bottom. The volume of the furnace charge expands when it comes into contact with the hot furnace gas. To accommodate this expansion and allow the charge to descend smoothly, the furnace body gradually widens from top to bottom. This design is to prevent “hanging,” which is a major problem in blast furnace operation. Hanging not only wastes furnace charge but, in severe cases, requires the furnace to be shut down for cleaning. A blast furnace is, in principle, a continuous production process. Once it is shut down, it takes a long time to resume production.

The finer the ore particles being smelted, the greater the gas flow at the edge, and the less likely the blast furnace is to hang. The flow of the edge gas is related to the angle of the furnace body. As the furnace charge descends, the heavier ore tends to descend vertically. When the furnace body angle is small, the ore will be far from the furnace wall, and a large amount of coke will move towards the furnace wall. At this time, a loose annular zone is formed near the furnace wall, which promotes the passage of a large amount of gas, forming a large gas flow. When the furnace body is too steep, the opposite happens—hanging occurs. Therefore, the angle of the furnace body is generally 86 degrees.

Below the furnace body is the bosh, a cylindrical section designed to eliminate the dead corners created by the furnace body. Below the bosh is the belly. As the coke burns, the furnace charge continuously melts, and its volume decreases. Therefore, its shape is larger at the top and smaller at the bottom. The belly angle is generally 76-82 degrees. A larger angle can reduce the friction of the furnace wall. At the same time, as the angle increases, the diameter of the hearth expands, the coke burns more fully, and the production efficiency of the furnace increases.

At the very bottom is the hearth, where the molten iron and slag accumulate. The temperature in the hearth is very high, and ordinary refractory materials are not enough. The temperature in the hearth is sufficient to melt the refractory bricks inside. The general practice is to install a cast steel or cast iron shell on the outer layer of the furnace wall, and then install a serpentine cooling water pipe in the shell to cool and protect the refractory bricks inside. Since steel is very difficult to cast—steel has poor fluidity—the industrial sector’s personnel studied it many times and felt that they were not confident in manufacturing such a large cast steel part. In the end, they decided to make a large cast iron cooling jacket as a second-best option. This casting alone took Xiao Bailang several months.

The tuyeres are located at the upper end of the hearth, eight in total. The nozzles must protrude into the furnace wall. Because they must withstand high temperatures, the nozzles are made of bronze. There are cooling water pipes inside the nozzles, and water is continuously supplied for circulating cooling during operation. The taphole is located near the bottom of the hearth, and above the taphole is the slag notch. They are also made of bronze and use circulating water for cooling.

The blast furnace is not only large in capacity but also operates continuously. The temperature at the throat of a large blast furnace is extremely high, so manual charging is not possible. Instead, mechanical automatic charging is used. There are several ways to charge a blast furnace. After discussion, Jiang Ye and Ji Wusheng decided to use the simplest mechanical structure, the charging bucket method. The charging bucket is bell-shaped. The hopper is transported to the top of the furnace, and then the charging bucket is lifted to the top of the furnace, where it clamps onto the furnace top. The furnace charge then leaks from the openable bottom of the bucket into the furnace throat. The hopper is moved on a track by a crank-link mechanism. Although this system is not complicated, it requires the industrial system to provide reliable equipment in terms of chains, mechanical transmission, and power machinery.

Jiang Ye said, “At first, Zhan Wuya said we should only build converters and import pig iron from Guangdong to make steel, not blast furnaces. I thought he was a bit right-wing and conservative—now it seems that even if we had wanted to build a blast furnace back then, it might not have been possible.”

“If we had built one then, it would have been a three-to-five-meter-high earthen blast furnace, producing two or three tons of pig iron a day, five tons at most. The charging would have been mostly done by winching the furnace charge up and then having workers shovel it into the furnace throat one by one. Not only would the workers have been half-roasted, but the charging would have been slow and uneven. The efficiency would have been as poor as that of the current small chemical plants,” Ji Wusheng said sympathetically of his namesake in the chemical industry. The industrial scale of his namesake’s enterprise was not even up to the standard of a county-level chemical plant in the 1970s in the old world. Many of its products were still at the laboratory level of manufacturing. If it weren’t for the coal coking combined production plant transported from the old world to make a show, the pitiful output of the 800-ton ammonia synthesis and electrolytic salt workshops would have made him roar at every Planning Institute meeting.

“Once our steel complex is put into production, we’ll probably be mass-producing chemical equipment. Your mechanical department will have a heavy burden.”

“What’s that to worry about?” Jiang Ye didn’t care. “Can we produce some special steel or something? Especially stainless steel. There are too many places where it’s needed. And silicon steel, for making generators, electric motors, and transformers. You don’t know how often Chang Gong comes to us crying that he has no place to use his skills in power construction.”

The Transmigration Group’s electricity supply was a major weakness. Whether it was power generation, power supply, or power use, it was probably at the level of a small county town in the late 1970s in the old world—or even worse. It was not even possible to build a county-wide power grid. And the direct result of the power shortage was the proliferation of steam engine boilers everywhere.

“Your request is a bit difficult. The former requires non-ferrous metals that we can’t get, and the latter is difficult to smelt. But manganese steel can be produced soon—the iron ore from Tiandu itself contains a relatively high amount of manganese, and there is also a manganese mine nearby that can be exploited,” Ji Wusheng said. “Besides, isn’t Chang Gong always planning the East Asian power grid’s ultra-high voltage transmission and transformation system, the Himalayan super power station, and the Yangtze River cascade power station development plan in his notebook? He can be an electrician and make plans at the same time.”

“Although it’s not as exciting as stainless steel and silicon steel, it’s still good news,” Jiang Ye said. Manganese steel has the characteristics of high strength and high wear resistance and plays an important role in many large machines. With manganese steel, the performance of the currently low-quality bearings, gears, structural parts, and connecting parts can be greatly improved. Manganese steel can also be used to make industrial cutting tools and provide high-quality weapon steel for the military industry.

Next to the blast furnace stood the completed large hot blast stove. The 125-cubic-meter blast furnace required a much larger blast volume than the previous small converters and melting furnaces. Larger often meant higher efficiency. A hot blast stove had already been built during the construction of the converter steelmaking workshop, and they had considerable experience in its construction and use. This time, with sufficient refractory materials, not only was the volume larger, but the internal structure was also optimized. The new hot blast stove was a standard Cowper-type hot blast stove, 10 meters high. The hot blast stove used the high-temperature waste gas from the blast furnace to preheat the air entering the blast furnace from the blower. The design goal was to have the outlet temperature reach 620°C. At such a high temperature, the reducibility of the iron ore would reach its maximum, and the coke consumption could be reduced by one-fifth.

“Engineer Jiang!” a naturalized citizen intern ran over in a hurry. “The gas plant construction site just called and asked you to take a look. There are some problems over there.”

“Okay, I’ll go right over,” Jiang Ye said, greeting Ji Wusheng, and went down the small hill. A farm vehicle was already waiting for him.

The gas plant was an important project of the Maniao complex. The coal coking combined chemical plant put into use in Bopu could also provide gas, but because it had subsequent chemical equipment to process the gas and tar produced during coking, the gas was generally consumed directly as a chemical raw material, and the small amount of surplus was used as fuel for the Bopu industrial zone nearby.

The gas plant did not need to use the coking brown coal specially transported from the Jiazi Coal Mine—the blast furnace coke was provided by the coal coking combined plant in Bopu. Instead, it used a special gas producer to dry distill various low-quality coals. Its production purpose was not to obtain coke, but gas.

After the gas workshop was completed, it would provide gas fuel for the entire plant area, and the main purpose was to provide fuel for the open-hearth steelmaking furnace—the gas produced in blast furnace smelting had a low calorific value and could not be used as fuel for the open-hearth furnace.

Unlike the special large coking ovens of the coking plant, the structure of the gas producer was simple and easy to operate. And the mechanical department also had a lot of experience in manufacturing and using gas producers. There was no difficulty in its manufacture and use.

After the coal was added to the producer, it was ignited for dry distillation. It reacted with the air added from the bottom of the furnace to produce gas. But at this time, the calorific value of the gas was low. As a fuel for the open-hearth furnace, its calorific value was too low. Therefore, while coking, the water vapor produced by the boiler evaporator was mixed with air in a certain proportion and then blown into the producer to produce semi-water gas. The calorific value of semi-water gas was much higher than that of air gas and could be used as fuel for the open-hearth furnace.

The tar produced during dry distillation was stored in a special tar tank and then transported to the coal coking combined plant in Bopu for further refining. Ji Tuisi planned to add a tar processing plant to the Maniao gas plant in the future to process the coal tar on-site and produce chemical products.