SLAG GRINDER DESIGN
CONTRIBUTING RE.ENGINEER
KnightHawk Engineering
www.knighthawk.com
CHALLENGE
Crushers and Slag grinders are often applied in Materials Handling and Gasification plants to reduce the size of quenched slag from the gasifier’s tap-hole or break clinkers from slow moving bed reactors. These clinkers are typically brittle and relatively easy to crush, but may be larger and very hard and abrasive when sintered during a reactor transient or upset conditions. Also, these crushers are often of toothed roller type, integrated in a pressure vessel subject to charge / discharge cycles, slow rotating yet transmitting very high torques and crushing forces. This makes it simultaneously a ‘machine’ and a ‘pressure vessel’.
A slag breaker dating from the 1970’s required replacement. The new design had to incorporate lessons learned in operations and maintenance, fit accurately into the existing structure and inlet-outlet flange face-to-face envelope, and re-use the existing drivetrain. The crusher must reduce slag as well as occasional refractory tiles or bricks, dislodged from the gasifier hot face, to no more than 1” in size to avoid bridging and arching in the outlet. The equipment must be designed, manufactured, tested and delivered to site under schedule constraints, in time for the next scheduled shutdown.
SOLUTION
KnightHawk engineering digitized hand drawn blue-prints and developed 3D CAD models (below) applied in concept development, client reviews and manufacturer reviews and design. Detailed 2D CAD drawings and part lists as well as geometry and meshing for Finite Element (FEA) designs, were developed from this model. The pressure vessel was designed as per ASME VIII Division 1 with supplementory analysis by FEA as per ASME/API 579-1 Fitness for Service (FFS) by using the methods and guidelines from ASME VIII Division 2 Part 5. The rotating parts and breaker element were integrated into the pressure vessel by shaft, breaker tooth, breaker plates, gland seals, end bearings and a bolt-on cantilever drive unit (not shown) consisting of a motor, gearbox and coupling. The breaker element is protected from overpower, including an auto reverse, circuit breaker, shear pin and hydraulic coupling.
RESULT
Successful design was achieved by: A multi-party, collaborative design process including original OEM Designer, Owner-Operator, KHE Specialty Engineering and Manufacturers all with significant experience in industry. A multi-disciplinary approach including process, mechanical, metallurgical and controls. A multi-physics approach including code ‘design by rules’, FEA ‘design by analysis’, 1st principle machine and structural design by correlations as well as fatigue, thermal and modal analysis…ensuring a design fit for purposes and with adequate protection against failure.