Chapter 806 - The Blast Furnace (Technical Chapter!)

The blast furnace was the most difficult part of the entire project. To construct it, a dedicated team was formed to gather all technical materials on blast furnace structure, materials, and construction methods. A 125-cubic-meter blast furnace, over ten meters tall and weighing several thousand tons, was the largest piece of industrial equipment the Elders had ever encountered. Its difficulty surpassed all previous industrial construction projects.

Structurally, a blast furnace must satisfy two prerequisites: charge materials must descend uniformly, and furnace gas must rise uniformly across all cross-sections at every height.

The uppermost part of a modern blast furnace is the throat, where charge is loaded into the furnace by specialized charging machinery. To protect the throat from damage by falling charge, a layer of steel bricks is installed. Once charge enters the throat, it is immediately dried and preheated by the hot furnace gases rising from below. The gases then exit through pipes at the furnace top—this section must be perfectly sealed to prevent the coal gas that comprises most of the furnace gas from leaking or escaping, which would cause worker poisoning.

A portion of the exhaust gas is recycled back into the blast furnace as fuel; the remainder is piped to the hot-blast stove to preheat the blast air.

The shaft is a cone with the smaller end at the top. As charge contacts the furnace gases, it expands from heat. To accommodate this expansion and allow smooth descent of the charge, the shaft widens from top to bottom. This design prevents hanging—a blast furnace's greatest operational hazard during combustion. Not only does hanging waste charge, but in severe cases, it requires a blowdown for cleaning. In principle, a blast furnace operates without shutdown; once blown down, it takes a long time to resume production.

The finer the ore particles, the greater the edge gas flow, and the less likely the furnace will hang. Edge gas flow relates to the shaft angle. As charge descends, heavier ore tends to fall vertically; when the shaft angle is small, ore moves away from the wall and coke migrates toward it. This creates a loose annular zone near the wall, promoting large gas flows. When the shaft is too steep, the opposite occurs—hanging develops. The shaft angle is typically set at 86 degrees.

Below the shaft is the belly, a cylindrical section designed to eliminate the dead zones created by the shaft. Below the belly is the bosh, which tapers from top to bottom because coke combustion continuously melts charge, reducing its volume. The bosh angle is typically 76–82 degrees. A larger angle reduces wall friction; additionally, a larger angle increases the hearth diameter, improving coke combustion and furnace efficiency.

At the very bottom is the hearth, where molten iron and slag accumulate. Hearth temperatures are extremely high; ordinary refractory materials won't suffice. The heat can melt the refractory bricks inside. The standard approach is to install a cast-steel or cast-iron outer shell on the wall, with serpentine cooling-water pipes embedded within to cool and protect the inner refractory lining. Because steel is very difficult to cast—its flowability is poor—the Industrial Sector team studied the problem extensively and concluded they couldn't reliably manufacture such a large cast-steel component. They settled on making a large cast-iron cooling jacket instead. Even so, this single casting alone occupied Xiao Bailang for months.

Eight tuyeres are mounted at the upper end of the hearth; the nozzles protrude into the furnace wall. Because they must withstand high temperatures, the nozzles are made of bronze, with internal water-cooling pipes for continuous circulation cooling during operation. The taphole is near the bottom of the hearth, with the slag notch above it. These too are bronze with circulating water cooling.

A blast furnace is not only large but operates continuously. The throat of a large furnace reaches extreme temperatures, precluding manual charging. Instead, mechanical automatic charging is used. There are several charging methods; after consultation, Jiang Ye and Ji Wusheng decided to adopt the mechanically simplest: the bell-and-hopper method. A bell-shaped charging bucket hauls the charge to the furnace top, where it locks into position. Charge then drops from the bucket's openable bottom into the throat. The hopper is driven by a crank-linkage mechanism sliding on rails. Though not complex, this system requires the industrial sector to provide reliable equipment for chains, mechanical transmission, and power machinery.

Jiang Ye said, "Back when Zhan Wuya said to skip the blast furnace and just run converters—importing pig iron from Guangdong—I thought he was being a conservative rightist. Now I see that even if we'd wanted to build a blast furnace then, we probably couldn't have managed it."

"If we'd tried back then, the best we could have done was a homemade furnace three to five meters tall. Maybe two or three tons of pig iron per day—five tons at most. Charging would have meant winching materials up, then workers shoveling them into the throat one scoop at a time—roasting themselves half to death in the process. Slow charging, uneven distribution. Efficiency like some podunk county chemical plant." Ji Wusheng commiserated with his compatriots in the chemical sector. By old-timeline standards, their operation didn't even match a 1970s county-level chemical factory; many products were still at laboratory scale. Without the coal-coking integrated plant shipped from the old timeline to bulk things up, the pitiful output of their 800-ton ammonia synthesis and electrolytic salt units would have them raging at every Planning Commission meeting.

"Once our steel combine goes into production, we'll be mass-producing chemical equipment. Your Machinery Department's burden won't be light."

"That's nothing," Jiang Ye said dismissively. "Can you produce specialty steels? Alloy steels? Especially stainless steel—we need it everywhere. And silicon steel too—for generators, motors, and transformers. You don't know how often Chief Chang comes crying to us about how useless he is in power construction."

The transmigration enterprise's electrical power was a fatal bottleneck. Whether in generation, transmission, or consumption, they were at roughly the level of a small late-1970s county town—or worse. They couldn't even form a county-wide grid. The direct result of the power shortage was steam-engine boilers everywhere.

"Your requirements are pretty demanding. For the first, we can't get the non-ferrous metals needed; for the second, the metallurgy is difficult. But manganese steel can come soon—Tiandu's iron ore naturally contains high manganese, and there's a manganese deposit nearby we can mine." Ji Wusheng said, "And besides, Chief Chang can just keep doing his county electrician work while planning his East Asia Power Grid super-high-voltage transmission system, Himalayan Super-Station, and Yangtze cascade development in his notebook."

"Not as exciting as stainless steel or silicon steel, but still good news," Jiang Ye said. Manganese steel had high strength and high wear resistance, with important applications in many large machines. With manganese steel, the currently poor-quality bearings, gears, structural components, and connectors could be greatly improved. Manganese steel could also be used for industrial cutting tools and to provide quality weapon steel for the military industry.

Beside the blast furnace stood the completed large hot-blast stove—the 125-cubic-meter furnace required far more blast than the previous small converters and melting furnaces. Bigger often meant higher efficiency. Having already built hot-blast stoves for the converter steelmaking workshop, they had considerable construction and operational experience. This time, with sufficient refractory materials, not only was the stove larger, but its internal structure had been optimized. The new hot-blast stove was a standard Cowper stove, ten meters tall. It used the blast furnace's hot exhaust gas to preheat the air entering via the blowers, with a design target of 620°C at the outlet. At such temperatures, iron-ore reduction would reach maximum efficiency, and coke consumption could be reduced by one-fifth.

"Engineer Jiang!" A naturalized apprentice came running over. "The gas workshop just called—they need you to come take a look. There are some problems."

"All right, I'll head over now." Jiang Ye said goodbye to Ji Wusheng and descended the little mound. A utility vehicle was already waiting.

The gas plant was an important component of the Ma'ao combine. The coal-coking integrated chemical plant at Bopu could also supply gas, but because it had downstream processing equipment to extract and refine the gases and tar produced during coking, the gas was generally consumed directly as chemical feedstock. The small surplus went to Bopu Industrial Zone as fuel.

The gas plant didn't use the coking lignite transported from Jiazi Coal Mine—the blast furnace coke was supplied by Bopu's coking plant—but instead used dedicated gas generators to dry-distill various grades of inferior coal. The purpose wasn't to produce coke, but gas.

Once completed, the gas workshop would supply gaseous fuel to the entire plant. Its primary purpose was to provide fuel for the open-hearth steelmaking process—coal gas produced during blast-furnace smelting had low calorific value and couldn't be used as open-hearth fuel.

Unlike the specialized large coking furnaces at the coking plant, gas generators had simple structures and were easy to operate. The Machinery Sector had considerable experience manufacturing and operating them up to now—no difficulties there.

Coal was loaded into the generator and ignited for dry distillation. Reacting with air blown in from below, it produced coal gas. But raw coal gas had low calorific value and was insufficient as open-hearth fuel. So while coking proceeded, steam from the boiler evaporator was mixed in proportion with air and blown into the generator to produce semi-water gas. Semi-water gas had significantly higher calorific value than air-gas and could serve as open-hearth fuel.

Tar produced during dry distillation was stored in dedicated tar tanks, then shipped to the Bopu coal-coking plant for further refining. Ji Tuisi planned to eventually equip the Ma'ao gas plant with its own tar processing facility to produce chemical products on-site.

(End of Chapter)