Marginal Column

A turn for the better

March 2014

 

A new hydraulic distributor, built by Woodings, distributes tons of raw materials inside a blast furnace – both quickly and precisely, right down to the last millimeter.

 
 

While the basic design of iron and coke blast furnaces is centuries old, today’s steel makers are looking for innovative ways to produce molten iron with increased production and efficiency. “The way iron pellets and coke are charged in layers inside a blast furnace really affects the melting process,” says Al Colucci, Vice President Engineering at Woodings Industrial Corporation, Pennsylvania, USA. “The layers are created by a system called a hydraulic distributor, using a chute located in the throat of the blast furnace to deposit raw materials in precise locations.”

The more accurately the chute can be controlled, the more precise the layers and the more efficient the blast furnace becomes. This is why one of Woodings’ key customers, a major Chinese iron and steel producer, wanted precise chute movement for their newest hydraulically controlled distributors. Up to this point, the customer had been using a hydraulic distributor of their own design on six blast furnaces.

However, these systems used a traditional hydraulic circuit with open loop control, which didn’t allow a high degree of chute control. The end-user called on Woodings to help increase accuracy and performance. The engineers were faced with a major challenge: the desired level of precision was difficult to achieve because tons of iron ore pellets and coke tumble down the chute.

Additionally the precise control happens while the chute rotates at 8 RPM – 7.5 seconds for each round. That constantly changes the loading on each of the four hydraulic cylinders. Adding to the challenge is the extremely demanding environment atop the blast furnace.

The hydraulically operated rotating distributor is extremely precise when layering input materials in blast furnaces. This is how up to 16 million tons of iron are smelted annually.

 

To carry out the project, Woodings worked together with Bosch Rexroth. “What made this project unique was the stringent specification on accuracy for an application with huge dynamic load changes,” says Charles Erdo, industrial machinery engineer at Bosch Rexroth in Bethlehem, Pennsylvania, USA.

“The control system has to react fast enough to maintain a very tight cylinder stroke tolerance between four differential area hydraulic cylinders.” The Rexroth solution, based on hydraulic engineering, commissioning and technology: high-response directional proportional valves, electronic pressure transducers, and control software for closed loop control.

To verify that the target accuracy and repeatability of the Rexroth hydraulics system would be achieved, Erdo involved Bosch Rexroth simulation groups in the U.S. and the headquarters in Lohr am Main, Germany. “The short, nine-month time window ruled out building a physical prototype to prove the concept to Woodings,” says Erdo.

Luckily the proprietary simulation tool MOSIHS (Modular Simulation of Hydraulic System) allowed simulation of a virtual model including the overall hydraulic system. The simulations verified the hydraulic circuit design and that the selected Rexroth components were optimal. In addition, the MOSIHS simulation showed that using a specialized spool flow characteristic control valve, control performance could be improved.

Based on these results, three final versions of the Woodings hydraulic distributor were assembled and tested at the company’s facility to confirm that the operation met all of the requirements. They were then disassembled and shipped to China for installation. “I can’t say enough positive things,” concludes Colucci. “When we put the system on the test stand, it performed exactly the way we wanted it to.”