System Mix Limited “The Solid Solution” SPECIALISTS IN SOLIDS MIXING
Sawtry Court Brookside Industrial Estate Sawtry Huntingdon PE28 5SB Tel: 01487 830123 Fax: 01487 832888 Email: firstname.lastname@example.org
STM Mixing System Operating Characteristics & Optimisation Control Philosophies: STM mixing systems are designed to provide flexible operating controls as each site has its own particular set of requirements. The following control sequences have been designed to provide the maximum amount of flexibility for site operators to maximise performance whilst minimising operation and running costs Basic Manual Operation Simply manually turn the system on and off as required with to other controls other than low level stop. Basic Timer Operation This is the most practical method of operation using run and delay timers to achieve optimum mixing with minimal control complexity and is most commonly used on sludge blending on a batching sequence or constant level and employs: • Hand Off Auto Simple selector switch to operate system automatically or manually ¾ Hand Operates the system continually overriding all other controls with the exception of low level shut off relay, as this will prevent dry running if system left unattended when emptying. ¾ OFF Set system to rest ¾ Auto Engages run and delay timers set to mix for a set period and rest of a set period (e.g. 1 hour ON 1 hour OFF) and works continually on this duty until the low level stop control is activated. The system remains stopped until level increases deactivating stop control and the timers then reset. ¾ Timers Timers are recommended to be manually adjustable to enable operations to trial different sequences to maximise performance whilst reducing running costs. Complex Timer Control This control sequence relies on a complex PLC login controller linked to level controls and is more likely to be employed on process controls where product is blended • Hand Off Auto Simple selector switch to operate system automatically or manually ¾ Hand Operates the system continually overriding all other controls with the exception of low level shut off relay, as this will prevent dry running if system left unattended when emptying. ¾ OFF Set system to rest
Continued Page 2
March 1, 2007
System Mix Limited “The Solid Solution” SPECIALISTS IN SOLIDS MIXING _________________________________________________________________________________ ¾
Auto Engages Run and Delay timers controlled by a PLC to mix and rest for variable periods dependant on the level and process stage, maintaining the maximum sludge blending where different sludge’s are being received and can be set on a 24 hr 7 day sequence to stabilise stored materials. This system requires an ultra sonic level control system to monitor and transmit data to the PLC and can have specific sequences programmed such as; fill, store and process sequences pre set and fully adjustable. Timers Timers are then in-built control sequences and fully adjustable to enable operations to trial different sequences to maximise performance whilst reducing running costs.
Setting a Basic Timer Control Sequence In this section we outline how to set the best sequence for mixing and what inputs are required from site personnel to achieve the optimum control regime. Controls Required Run timer Fully adjustable 10 – 600 minutes Delay timer Fully adjustable 10 – 600 minutes Low level stop Either independent float switch or linked to existing sludge level control if Ultra Sonics are employed already and accessible. Initial Delivery Settings We recommend that the initial sequence be set to 1 hour ON and 1 hour OFF and pre-programmed at the time of panel manufacture, as this will cater for most applications Adjustment to Optimise Control Sequence Once the system has been filled and the sludge has been processed correctly for at least 2 weeks, operators are urged to carry out some simple tests to achieve maximum potentials from the system. 1. Fill the tank to its maximum operational capacity. 2. Blend tank contents for 90 minutes, by operating in Hand mode, sample the sludge at the end of this period and record the DSC. This is the bench mark or control sample. 3. Turn system OFF and leave to stand for 1 hour and re-sample. 4. R record the DSC, this value provides a figure for settled DSC after 1 hours rest. 5. Compare values; if sludge DSC increases to 1.2 times greater than control sample, 1 hour is delay setting. If it does not, repeat sample tests at hourly intervals until the 20% increase has been achieved, and set the corresponding period as Delay Timer setting. 6. Once delay settings have been determined (indicating the settling index of sludge) repeat the process for the run timer, this time sampling every 15 minutes at the start of the 1 hour mix sequence. 7. Record the DSC of each sample to determine when the contents meet the homogenous blend recorded in control sample.