Project Name: 600,000-ton Push-Pull Type Pickling Line

Customer Name: Shandong Dongding Steel Rolling Co., Ltd.

Project Nature: New Construction Project

Contracting Method: General Contracting by Jingjie Ruisi

Contract Date: May 7, 2011

Production Status: Under Construction

Operation Status: Good

I. Description of the Pickling Process Flow

This pickling line is a push-pull type pickling line, adopting the currently advanced shallow tank turbulent pickling technology. The process equipment and technology provided are proven reliable, advanced and mature through production practice, and can meet the buyer's requirements for stable production and long-term operation as a complete set of equipment and technology. This technology features a reasonable equipment structure, high operation efficiency, low production consumption, convenient operation, and few equipment operation faults.

The designed pickling line completes the entire process of steel strip pickling treatment from uncoiling to recoiling online. At the entrance of the line, there is a loading trolley. The steel coil is first placed on the receiving stand by a crane, and then the loading trolley transports the steel coil to the pre-uncoiling roller for pre-uncoiling (including straightening the head, cutting the head and corner). Subsequently, the loading trolley transports the steel coil to the center position of the uncoiling machine's reel. The uncoiling machine of the line adopts a cantilever type uncoiling machine. The expansion and contraction of the uncoiling machine's reel is driven by a hydraulic cylinder set at one end of the reel's core shaft. The uncoiling machine frame is driven by a hydraulic cylinder and can move on the base to adjust the center position of the steel coil during uncoiling. To ensure the straightness of the steel strip during threading, a straightening machine is set at the entrance of the line.

After the steel strip enters the pickling tank, the surface of the steel strip directly undergoes the following chemical reaction with the hydrochloric acid solution in the tank: Fe203+6HCI===2FeCl3+3H2O

Fe304+8HCI===2FeCl3+ FeCl2+4H2O

Fe0+2HCI===FeCl2+ H2O

Fe+2HCl===FeCl2+H2

The pickling tank is divided into five sections. The tank body is made of carbon steel and lined with chloroprene rubber and double-layer granite strips. This structure can prevent the rubber layer from being damaged when the granite lining is maintained or replaced. Between each section of the tank, there are acid squeezing rubber rollers and acid isolation chambers. The bottom of the tank is lined with granite and the lower roller surface of the squeezing rubber roller is at the same plane. A fiberglass tank cover is installed above the steel strip running plane and the tank is sealed by a water seal. The squeezing roller is driven by a variable frequency motor and the position of the leading edge of the steel strip during the threading process can be detected by the change in motor current to avoid overlapping and piling up of the steel strip in the acid tank. Each section of the acid tank is equipped with a set of acid circulation heating system. The acid is heated by a vertical graphite heat exchanger. At the same time, with the help of the tank structure, the acid flows rapidly in a turbulent form, which greatly increases the pickling speed. Fresh acid is replenished from the No. 5 acid circulation tank and is gradually replenished to the previous sections through the liquid level control system of the acid circulation tank. Finally, the acid in the No. 1 tank is discharged to the waste acid collection tank. Since each section of the acid tank is relatively isolated and operates independently in a circulation, the concentration gradient of each section can be effectively controlled. The first section of the cleaning tank is independently cleaned and the rinse water is discharged to the acid mixing tank. The remaining four sections use circulating spray rinsing (condensate water). Fresh water is replenished from the No. 5 rinse tank and the rinse water flows from the bottom water collection tank of the cleaning tank from the fourth section to the second section, and is finally discharged from the overflow port of the second section to the rinse water collection tank. The entire pickling tank and cleaning tank are controlled under a slight negative pressure. The acid mist is drawn through the exhaust pipes set at the inlet and outlet of each section to the acid mist scrubber of the waste acid regeneration station, where it is washed by spray and discharged outside the factory. The steel strip drying is carried out by a hot air dryer, and the hot air is heated by a steam heat exchanger. The steel strip edge trimming is done by a cantilever disc shear, and a pinch pass centering machine (CPC) is set at the entrance of the disc shear to control the edge trimming centering. The trimmed waste edges are wound into waste edge balls by a waste edge winder. The winder is a cantilever tension winder and the winding tension is established by a three-roll tension machine. The winding is equipped with an EPC control to ensure the edge alignment of the wound coil. At the exit, a hydraulic-driven uncoiling trolley is used to transport the steel coil to the unloading rack.

The electrical control system of the unit consists of a power distribution system, AC variable frequency motor drive device, AC motor control unit, PLC operation control system, main operation console, sub-operation console, and uncoiling industrial monitoring system. The operation control of the system is completed by the PLC programmable controller, and the operation system also includes the interlocking control of the auxiliary process systems of the pickling unit.

II. Design Basis

Raw materials: Hot-rolled plain carbon steel, deep drawing steel, low alloy steel

Steel grades: Q195, Q215, Q235, 08F, CQ, DQ, DDQ, etc.

Production capacity: 600,000 tons/year

Annual operation plan: 7,200 hours

Raw material weight: Max 26,000 kg/coil

Inner diameter: Φ610mm, Φ762mm

Outer diameter: Φ2100mm

Width: 800 - 1300mm

Thickness: 1.8 - 4.0mm

Finished product weight: Max 26,000 kg/coil

Inner diameter: Φ610mm, Φ508mm

Outer diameter: Φ2100mm

Width: 800 - 1250mm

Thickness: 1.8 - 4.0mm

Uncoiling tension: 18kN

Winding tension: 60kN

Process method: Push-pull shallow tank turbulent hydrochloric acid pickling

Total length of acid tank: About 68m

Pickling medium: Hydrochloric acid (≥31%)

Pickling concentration: 8 - 18%

Pickling time: 26s

Pickling temperature: 65 - 85℃

Maximum acid concentration: 200 g/L HCl 120g/L   Fe2+

Change roll time: Unwinding section max: 2.0 min, Winding section max: 1.5 min

Product form: Roll to roll

Drive mode of the unit: AC drive, variable frequency speed regulation

Layout of the production line: From the operator's side, the production line is from left to right

Energy: Water, electricity, steam

Unit speed:

Pickling process speed: max 150 m/min

Feeding: 10 - 80 m/min

Loop storage:

Entry: None

Exit: 30 m

III. Process Flow

Pre-unwinding preparation station: Receiving table → Unwinding trolley → Ground roller unwinder → Three-roller straightener with pinch rolls → Corner shears → Hydraulic shears → Scrap hopper (Features: Reduces the preparation time of the unwinding section and effectively utilizes the pickling unit). Pickling unit: Unwinder (with pressure roller, reverse bending roller) → Unwinding scraper → Steering pinch rolls → Vertical guide rolls → Three-roller straightener with pinch rolls → Cross-cut shears → Vertical guide rolls → Pre-cleaning tank (900 mm, 2 squeeze rolls) → 5-stage hydrochloric acid pickling tanks (5 x 13.5 = 67.5 m) → 5-stage water washing tanks (including pre-cleaning section) → Edge blower → Hot air dryer → 2# pinch rolls → Loop (with loop swing tables at both ends) → Vertical guide rolls → Pinch roll alignment machine → Rotary shears (with scrap roll-up machine) → Three-roller tension rolls → Cross-cut shears → Vertical guide rolls → Steering pinch rolls → Winder → Unwinding trolley → Receiving table