Method for starting and igniting a sulfuric acid boiling furnace

In our plant, sulfuric acid is produced from 60,000 tons of pyrite. The process of ignition involves preparing dry ore with a sulfur content of around 20%–25% and a moisture content of less than 5%, ensuring that the thickness of the ore layer lies between 400–600 mm. One ton of diesel, as well as cotton yarn and rags, are also required. Ignition equipment such as oil guns, air compressors, and oil pumps must be ready, along with a rake for moving the ore and various personal protective equipment. Once the preparation is complete, ignition can begin; if the furnace has been shut down for a long time, it also needs to be dried out. Those with a short duration can be ignited directly. First, conduct a test on the resistance of the air cap; it should generally be below 260 mm of water column, otherwise the air cap needs to be cleaned. Second, after laying the ore, conduct a cold boiling test; it is essential to level it out, otherwise ignition will not be possible. Once it has been leveled, ignition can proceed; use an oil gun to blow at the torch so that the ore layer burns evenly, with little difference in temperature across various areas, allowing the temperature to rise steadily. When the temperature reaches around 400 degrees, the furnace door can be closed and the chimney on top of the baking furnace can be shut. As the temperature rises, ore can be added appropriately, and it can be stirred around using a rake.

I have operated furnaces for producing acid from 80,000 tons of sulfur-rich concentrate: first, clean the air caps of the boiling furnace, then spread 350–400 MM of dry powder ore containing about 15% sulfur and conduct a cold boiling test. After leveling it out, add about 100 MM of dry wood on top of the ore layer, light a fire, seal the furnace door while leaving an oil gun hole open. When the wood has burned down to about 3/4 of its volume, inject diesel fuel and start the blower to supply additional air. Once the temperature at the lower layer of the boiling zone reaches 400 degrees, remove the oil gun, seal the furnace door, and start the main blower; the auxiliary blower supplies air, while the main blower adjusts its operation to maintain balance. When the temperature of the boiling zone starts to drop after reaching its peak, add more ore to the furnace. Control the temperature and follow the standard operating procedures

I have operated a 60,000-ton furnace for producing acid from pyrite: Materials: dry fine river sand, 500 Kg of charcoal (broken into small pieces). Steps: Clean the air cap； Spread dry fine river sand to completely cover the entire wind cap by about 3 cm or more ； Cold boiling experiment passed ； Lay a layer of small pieces of charcoal, about 5 CM in size ； Then, spread the burning charcoal on the outside evenly inside the boiling furnace ； Seal the furnace door ； When the temperature at the bottom of the furnace reaches around 300 degrees, start the blower to create a slight positive pressure. Once the temperature begins to drop after reaching its peak, add ore while keeping the water color brownish-red; careful operation is required. Wait until the pressure at the bottom of the furnace returns to normal before discharging the slag. This is just my personal opinion for reference only

Sulfur is the best choice for lighting a small boiling furnace; during ignition, the flue gases go directly into the conversion system, resulting in no pollution at all. Moreover, the ignition process takes only half an hour.

Wood + diesel ignition method: The boiling furnace used in our plant for producing acid from 60,000 tons of pyrite has a roasting area of 8.3 square meters. The process of ignition is as follows: Prepare dry ore with a sulfur content of around 18%–24% and a moisture content of less than 4–5%, with particle sizes under 3 mm; ensure that the thickness of the ore layer is between 400–500 mm. Also needed are 2–3 tons of diesel, one ton of firewood, along with cotton yarn, rags, etc. Ignition equipment such as oil guns, air compressors, and oil pumps must also be prepared, along with a rake for moving the ore and various personal protective equipment. Once the preparation is complete, ignition can begin; if the furnace has been shut down for a long time, it also needs to be dried out. Those with a short duration can be ignited directly. I. Conduct proper tests on the resistance of the air cap; it should generally be below 200–260 mm of water column. Before ignition, the air cap must be cleaned (by using a welding rod to clear the ventilation openings), and the furnace chamber must also be cleaned, ensuring that there are no wires or metal shavings present. II. First, spread red slag that has been sieved to 3 mm thickness around the wind cap; it must cover the wind cap completely and be leveled. Then, lay wooden planks inside the furnace and spread the material used for ignition on top, with a thickness of about 500 mm. After that, conduct a cold boiling test – the surface must be perfectly flat; otherwise, ignition will not be possible. After it has been leveled, add 1-2 tons of small wood chips on top, and then the fire can be started. Once the wood chips have burned out, use an oil gun to spray oil in order to raise the temperature. The heating of the ore layer should be even, with little difference in temperature between different areas, allowing for a steady increase in temperature. When the temperature reaches around 400 degrees, the lower ignition furnace door can be sealed and the chimney on top of the calcination furnace can be closed. As the temperature rises, ore can be added appropriately, and it can be stirred around using a rake.

I visited a sulfuric acid plant by the Yangtze River (which burns pyrite) and saw their furnace startup process: the preparatory work before starting up is more or less the same – mainly cleaning the air nozzles, then covering them with a layer of dry red slag, conducting a cold boiling test, and leveling it out. Add more firewood; once the height of the firewood reaches half of the entire boiler, light a fire and close the boiler door. When the wood has burned down to about half, the temperature inside the furnace reaches roughly 800 degrees. At this point, the fan is started immediately and ore is added; slag is then removed once the pressure at the bottom returns to normal levels.

Ash transfer for ignition method: Some companies have more than one process for producing acid from pyrite; while one set of the systems is in operation, another set is shut down for major maintenance, and after the maintenance is completed, it needs to be ignited and brought back online. Once the preliminary preparations are complete, the method of transferring ash for ignition can be used: specifically, a quantity of burned red slag at a temperature of 500–600 degrees Celsius is transferred into the furnace that is ready to be started up; the amount used depends on the requirements. The furnace door is then sealed quickly, the air supply is adjusted to a low level to ignite the system, and dry mineral powder is added according to the conditions inside the furnace. Two families used this driving method on a regular basis; it allowed them to save a significant amount of diesel costs, had low operating expenses, a short ignition time, and fast speeds.

The method mentioned on floor 8 is very good. Our factory has two systems; in the past, both systems used the same type of ore (pyrite), and the method mentioned on the 8th floor was applied. Now that we have upgraded to a new system for burning sulfur-rich sand, and with a significantly increased scale of operation, we no longer use this method. I have also heard from colleagues who visited our factory talk about this method; it’s quite feasible. It can be widely promoted.

In our factory, when starting the furnace, we first load the red slag into it, then seal the furnace door before lighting it

Everyone I talked to said it’s good; each factory has its own methods – diesel, firewood, sawdust, cottonseed shells, charcoal, and so on. Our factory uses charcoal for ignition (with an empty furnace). First, a structure is built 200–300 mm above the air cap using bamboo and bamboo strips; the strips should be broken into pieces 20–30 mm wide, with their length determined according to the size of the furnace. Charcoal is then placed on this structure at a rate of 100 pounds per square meter; the charcoal needs to be crushed first. The door is sealed, leaving an ignition hole of 200×200 mm at the bottom. A torch is then used to ignite the bamboo strips, after which the ignition hole is closed. At this point, both the fan and the exhaust system are turned on. Once the temperature in all areas reaches around 200–300 degrees, the fan is started, with the airflow initially set at a low level. As the temperature rises, the airflow is increased. After the temperature reaches 1000 degrees, it drops back to around 800–900 degrees. The exhaust chimney is then closed, and air is supplied to the system. Material is then added gradually, while the pressure at the bottom of the furnace is increased step by step, until the system operates normally.