Crushers and slag grinders are often applied in materials handling and gasification plants to reduce the size of quenched slag from the gasifier’s taphole 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 reactor transient or upset conditions. Also, these crushers are often a toothed roller type integrated in a pressure vessel subject to charge and discharge cycles, slow rotating yet transmitting very high torques and crushing forces.
Recently, a plant’s slag breaker dating from the 1970s 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 one inch in size to avoid bridging and arching in the outlet. The equipment must be designed, manufactured, tested and delivered to the site under schedule constraints in time for the next scheduled shutdown.
KnightHawk Engineering (KHE) digitized hand-drawn blueprints and developed 3D computer-aided models (CAD) 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 supplementary 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 seal, end bearings and a bolt-on cantilever drive unit 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.
The breaker element and teeth must be accurately sized and designed for particle size reduction, throughput and slag crush strength requirements to ensure effective crushing, yet avoid jammed rotor and lockup conditions. KHE determined the required grinding energy by the third comminution theory as per American mining engineer Fred C. Bond’s equation using a "work index" to define motor horsepower, torque and crushing power requirements gleaned from experience for this type of equipment.
The pressure vessel design must include considerations of internal pressure-temperature design, fatigue loading from batched feed and pressure cycles, bending and crushing forces from drivetrain weight and work, thermal loading from batch cycles and modal analysis to ensure no coupling between any fundamental natural frequency, function and any of the forcing functions or excitations from the rotating parts result in resonant vibrations.
Materials, stainless steel and tungsten-carbide weld overlay of internal surfaces subject to corrosion, impact, crushing and flow-erosion must all be carefully selected to provide a robust, yet manufacturable and cost-effective equipment fit for service over its design life.
The seal design must include effective sealing against varying pressure-temperature conditions, and a seal flush to ensure cooling, lubrication and avoid intrusion of abrasive particles. This seal design is typically a multi packing ring compressible gland type with lantern ring assembly. The seal acts in the annular space between the shaft-nozzle housing and the rotating shaft. The nozzle bore is weld overlayed in stainless steel and finally machined to diameter and surface finish presenting the outer seal surface. A shaft sleeve is located by a key, retaining washer and threaded lock nut. This shaft sleeve is located by the breaker teeth hub. An inner compression ring is then bolted to the housing. Sealing between the shaft sleeve and the shaft, preventing slurry intrusion and leakage, is provided by two O-rings.
For more information, visit knighthawk.com or call (281) 282-9200.
