What are the Three Stages of Pyrolysis?

In an industrial pyrolysis system, the process is practically defined by three key operational stages: feeding the reactor, condensing the oil, and discharging the carbon black. Each stage is crucial for the continuous and efficient conversion of waste materials, such as tires or plastics, into valuable products.

DOING pyrolysis plant process

First stage: feeding of raw material

Prepared feedstock, like tire chips or plastic shreds, is conveyed into the reactor. This step is carefully controlled to ensure an oxygen-free environment, which is essential for the pyrolysis reaction to occur instead of combustion. Once sealed and heated, the material inside begins to thermally decompose as temperatures rise.

DOING offers customized feeding solutions to match the operating philosophy of each pyrolysis unit.

1.1 Batch Pyrolysis Plant:

In our batch pyrolysis systems, the feeding process is a separate operation. Whole tires or plastic waste are loaded into the reactor. (Alternatively, pre-treated feedstock, such as shredded tires or plastic chips, can increase feed volume and improve pyrolysis efficiency to some extent.) This is typically done manually or with a simple mechanical feeder. Crucially, the reactor is sealed before heating begins to ensure an absolutely oxygen-free environment throughout the pyrolysis cycle. This approach prioritizes ease of operation, making it ideal for small pyrolysis plants or units that require handling multiple feedstocks and where flexibility is critical.

1.2 Semi-Continuous Pyrolysis Plant:

Our semi-continuous pyrolysis plants employ a more streamlined feeding method, directly feeding the reactor via an automated feeder, which requires pre-treatment of the raw materials. A key feature is the use of a sophisticated sealing mechanism, typically including a screw feeder, to maintain an oxygen-free environment during feeding.

1.3 Continuous Pyrolysis Plant:

Our continuous pyrolysis plant is designed for maximum efficiency and large-scale industrial applications, equipped with a constant and automated feed system. Pretreated feedstock is continuously conveyed into the reactor via a screw conveyor. Sealed designs at the feed inlet and upstream processing ensure complete prevention of oxygen ingress, even with a constant material flow rate.

DOING pyrolysis plant feeding devices

Second stage: condensation of oil vapor

The intense heat inside the reactor (typically between 200°C and 400°C) breaks down the long polymer chains, releasing hydrocarbon vapors. These hot gases are then piped into a condensation system, often a series of cooled condensers. Here, the vapors are liquefied into a stable, dark fuel oil, which is collected in storage tanks for later use or refinement.

The condenser unit is a critical piece of equipment in the DOING pyrolysis plant, responsible for rapidly cooling the oil and gas produced by the cryogenic pyrolysis of waste through circulating cooling water, ultimately liquefying it into fuel oil. Our pyrolysis units are available in both tubular and tank-type configurations, each with its own focus on cooling efficiency and practical applications.

2.1 Tubular Condensation System: This sophisticated system comprises multiple stages of vertical/horizontal condensers and oil-water separators, totaling seven condensation processes with a total cooling area of 100 square meters. Through multiple pipes and a precise condensation design, cooling efficiency is significantly improved, ensuring no waste of oil and gas.

DOING pyrolysis plant tubular condensation system

2.2 Water Tank Condenser: This system features an integrated block structure with multiple internal pipes of varying sizes, designed at a specially designed tilt angle angle to facilitate oil and gas flow and condensation. Compared to the shell-and-tube type, its structure is simpler and installation and maintenance are more convenient.

While both types offer excellent condensation performance, DOING recommends choosing the most suitable condensation system based on factors such as site conditions, maintenance needs, cost budget, and the type of pyrolysis feedstock (e.g., for plastics prone to wax formation during pyrolysis, a water tank condenser is recommended).

DOING pyrolysis plant water tank condenser

Third Stage: discharge of carbon black

After the oil-producing vapors have been driven off, the solid residue left inside the reactor is primarily carbon black and steel wire. Once the reactor cools, this solid material is safely extracted. The carbon black can be further processed and sold as a reinforcing agent in rubber manufacturing or as a pigment.

In the waste pyrolysis process, the slag removal stage is crucial for achieving resource utilization and continuous, stable equipment operation. DOING Company has designed diverse slag removal solutions for pyrolysis plants of different sizes and levels of automation to meet the individual needs of customers and ensure high efficiency, safety, and automation.

3.1 Batch Pyrolysis Plants

Batch pyrolysis plants typically require slag removal after shutdown. The location and method of the slag removal ports are mainly divided into front slagging and side slagging.

Side Discharge: A slag removal port is installed every 180° on the side of the batch reactor. After the reaction is complete and the equipment cools, the carbon black is discharged from the side.

DOING batch pyrolysis plant side discharge

Front Discharge: After the reaction is complete, the equipment needs to be cooled to a safe temperature. Then, the operator opens the front discharge removal door to discharge residual materials. For materials like steel wire, it can often be pulled out directly. For the remaining carbon black or aluminum from the pyrolysis of aluminum-plastic materials, the reactor is typically inverted. During feeding, the internal spiral structure conveys the feedstock towards the rear; when inverted for discharge, this spiral reverses its action, conveying the material forward and out of the front port.

3.2 Semi-continuous pyrolysis plant

High-Temperature Rear Discharge: In a semi-continuous pyrolysis plant, carbon black can be discharged at high temperatures during the production process. The carbon black produced by pyrolysis is first discharged through a small reactor and then via a screw conveyor.

The slagging outlet is located at the rear of the reactor. The equipment is designed with a sealed structure, typically employing high-temperature resistant screw conveyors (augers) combined with advanced sealing technology to achieve continuous slag discharge under high-temperature conditions.

Compared to batch pyrolysis plants, semi-continuous pyrolysis plants have a higher degree of automation in high-temperature post-discharge slag removal, reducing manual intervention, shortening slag discharge time, and improving overall equipment production efficiency.

DOING semi-continuous pyrolysis plant high temperature rear discharge

3.3 Fully Continuous Pyrolysis Plant:

Carbon Black Elevator Screw Discharge:Fully continuous pyrolysis plants represent the most advanced pyrolysis technology currently available. They achieve continuous operation from feeding to slag discharge, maximizing production efficiency and automation.

In a fully continuous pyrolysis plant, carbon black is continuously conveyed from the reaction zone. Multiple high-temperature resistant, high-strength screw conveyors (augers) are connected to the bottom of the reactor. Once carbon black is produced, the augers begin to rotate, continuously lifting and discharging the carbon black from the rear of the reactor. The entire slag removal process is fully automated and continuous. The auger's inlet and outlet are designed with a highly efficient sealing system, which effectively isolates external air, prevents oil and gas leakage, and ensures that the internal high-temperature environment is not disrupted. At the same time, the auger's outer pipe also has circulating cooling water to assist in cooling the carbon black. The discharged carbon black is transported by the auger to an external collection system for further cooling and collection, preparing it for subsequent processing and utilization.

DOING continuous pyrolysis plant carbon black elevator screw discharge

The three-stage framework of feed, condensation, and discharge provides a practical framework for industrial pyrolysis plant processes. Combined with feedstock pretreatment, environmental protection, and safety systems, this model ensures stable operation and economic benefits for the pyrolysis plant. If you are evaluating waste pyrolysis solutions, DOING Company can customize each stage based on your feedstock, throughput, local regulations, and target products to provide you with a robust pyrolysis system.