We are nearly constantly bombarded with internet messages, news articles and advertising promoting the concepts of “going green,” or as many companies have now adopted the moniker of “sustainable operations.” Regardless of the catch word or phrase, the message is all about reducing the energy we consume in our daily operations. Yet, in the midst of all this chatter, process and automation designers still continue to overlook a key combination of energy consumers in nearly every process design; pumps to move fluids and the control valves that regulate flow.
The pump-valve method of moving and controlling fluids has been around for a long time. And in every case, we apply far more energy to the process than is necessary to move the fluid from one location to another because the control valve consumes a large amount of the energy to control the flow. This design developed because motors, at the time, were designed to operate at a single speed, so to control the flow of the fluid, a control valve was required. Amazing though, we still see almost every new process facility being designed and built today using this same basic energy-wasting control feature.
In this time of sustainability, I find it hard to believe that this is still happening. The problem of a fixed speed motor was solved decades ago with the invention of variable speed or variable frequency drives (VFDs). I would guess that most of us that apply automation to processes are aware of these devices even if we perhaps don’t know much about them, but perhaps it’s time we learned. By varying the speed of the motor, we are able to vary the head produced by the pump which can be used to directly control the flow of the fluid without a control valve. As a result, only the necessary energy to move the fluid from one point to another is applied, saving upwards to 40% or more of the energy used today. When you consider how many pump-valve combinations are installed across the world today, we are looking at a very large quantity of energy that could be saved.
VFDs are no longer bleeding edge technology. With energy reduction a key objective of almost every manufacturing company, it’s time to get onboard with a new design philosophy of using VFDs to eliminate the waste that control valves bring to the process. And for those brave enough to make the leap, there are a number of peripheral benefits: among them reduced capital requirements for the motors due to lower horsepower requirements, eliminating the capital cost of control valve stations (control valve, block valves, bypass valve, additional piping, welds, …); eliminate maintenance on the valves and in volatile hydrocarbon service, the testing and reporting required for the packings; and in many cases eliminating the need for gearbox capital costs and maintenance with the use of direct-drive motor configurations.
Granted, there are applications where control valves will still be required, but even if half the applications in new facilities or expansions were done with VFDs, there would be a very noticeable impact on energy usage, and capital and lifecycle costs for those of you willing to make such a change.
For those readers that may have already started down this path, why not share you success stories in the comment section of this blog so other readers might benefit from your experience.