Corporate Australia is in the midst of a productivity offensive. Shareholders and boards across the country are pressuring their management to get more out of less, whilst drying up the funds available to do so. ‘Capital light’ is turning out to be an astute catchphrase for the New Year. It is clear that getting the most out of existing operations is key to enterprise survival in this paradigm. This pressure is now flowing to the engineers tasked with operating the revenue generating activities.
As we saw in the last blog Targeted Plant Maintenance and Smart Instruments, replacing older equipment with smart instruments can reduce the opportunity cost of performing maintenance activity, albeit at a modest increase in initial capital cost. The higher initial equipment cost is often recovered through productivity improvements due to the superior functionality of the new equipment over that which it replaced. Significant productivity and efficiency improvements are achievable through multiple smaller changes such as installing Variable Speed Drives (VSDs) or smart control valves rather than major infrastructure changes. However the pitfall with conducting upgrades is determining which combination of changes will provide the maximum productivity improvement and minimise tertiary impacts to the asset as a result of the change. This is no easy feat whilst conforming to a ‘Capital light’ directive.
For those looking to reduce their energy consumption, VSDs can be a very attractive option. Variable processes which are currently run by induction motors, whose speed is dependent on line frequency are an ideal candidate for a VSD. Without the frequency and voltage manipulation offered by a VSD, induction motors are limited to operate close to a multiple of the utility line frequency and the number of magnetic poles in its stator. Hence energy is wasted where the existing process runs with the motor at its rated speed and the process is throttled by another means such as valves or shutters.
Whilst the energy savings can be an attractive inducement to installing VSDs, care must be taken to ensure they do not interfere with the operation of existing equipment in the plant. The large transient currents and frequency harmonics generated by VSD units can introduce sufficient electronic noise which could cripple other unrelated equipment. A raised or noisy ground potential can confound efforts to determine the interference path. Upgraded wiring, physical isolation and signal filtering are necessary considerations to be made when designing and installing VSD units.
Installation of smart instruments can provide more than just better maintenance outcomes. Their health reporting functions give operators greater confidence in the veracity of their output. Combined with smart control valves with position feedback, tighter tolerances can be achieved in process variables. This increased confidence can allow processes to be run closer to their limits and allowing greater yield from existing rates of supply. Unless you’re looking at replacing all actuators and instruments in the plant, careful analysis is required to ensure that the right equipment is being targeted for replacement.
Plant design and current operations may dictate that process control is achieved by modulating a particular valve in reference to a specified instrument. However, given the tighter tolerances sought, what dependencies exist elsewhere in the system that also need to be addressed? The very pressure, temperature or flow variations that you sought to eliminate may have been introduced by your control system in response to the actions of other, seemingly unrelated equipment. Replacing individual instruments and imposing new control strategies may yield no benefit for the capital outlay or worse – it may have detrimental effects elsewhere in the plant.
How any of these upgrades interacts with your existing network and control systems are also vital considerations. You may find that actually making proper use of the extra data generated is beyond their capabilities. Even small changes in any area of your plant may also require a complete overhaul of your existing safety system. Whilst ‘Capital light’ strategies reduce the expenditure on equipment, they come with the requirement to ensure that a diverse team of appropriately skilled professionals are engaged to affect any upgrade. Delivering optimised operation of complex modern systems for minimal expenditure is no small feat. Applying this system-wide approach is a highly effective risk mitigation strategy to achieve the greatest cost benefit from a low capital investment strategy.
Read more by James Wall
Reducing Risk of Customer Plant Upgrades co authored by Gilbert Liu