By C. Correia, N. Ventress, L. Escobar-Ferrand, and S. O’Grady
Water and wastewater treatment applications encompass a wide range of processes, technologies, and physical/chemical methods. Among them, filtration and separation technologies are the core of treatment processes, and in many cases, they can be critical process bottlenecks. Engineering firms, engineering procurement and construction contractors, and end users have high expectations regarding a plant's operation, process design, efficiency, and performance. Normally, most filtration units are packaged on steel frame skids (see Figure 1). It is critical for these skids to be properly designed. They must contain the correct components for accurate diagnostics and system troubleshooting. After all, these systems normally run 24/7.
Advances in control technology—particularly at the electrical terminal with input/output (I/O) devices and the pneumatic pilot valve terminal—allow integrated point diagnostic information to be available locally via supervisory control and data acquisition, integrated Web server, or accessed remotely over an Ethernet connection.
The burden of the filtration equipment manufacturer
Original equipment manufacturers (OEMs) normally struggle to provide an optimal service package and technical support to their filtration skids. This is especially true for membrane filtration skids. Field service is expensive—think travel costs and staffing—and time-intensive for travel to remote locations. In addition, some OEMs decline to participate in bids and public tenders due to the challenges of providing a proper service package.
Today, when an OEM is awarded with a project that includes a filtration skid, such as membrane filtration, ultrafiltration, reverse osmosis, or chemical dosing, that OEM has typically offered an attractive warranty and a strong service contract. Service contracts and warranties are set up in several ways and under different forms, such as a hotline with 24/7 technical support, guiding and supervising the commissioning, startup, and personnel training, regularly scheduled visits for cleaning and troubleshooting, and scheduled preventive maintenance. The selected strategy varies depending on the capacity of the plant, location, personnel, budget, and accessibility but usually includes as the first criteria remote diagnostic capabilities that naturally serve as a key ingredient to maintain continuous production with reduced downtimes, smooth operation, and optimal performance.
Expectations of filtration equipment customers
Figure 2: Many field devices can be connected to a single remote terminal as shown in this process control cabinet.
Customers have high expectations about their process systems. So offering an efficient, detailed, and expedited remote diagnostics system is critical for a quick and successful response. These systems must cover as many components of the skid as possible so all the likely alerts, alarms, sequences of operation, and critical processes like backwashes, integrity tests, or clean-in-place functions can be identified, tested, and observed.
Conducting a detailed remote diagnostics program can troubleshoot and correct problems and issues approximately 80% of the time. It is especially important to remember that most of skids are located in remote areas with limited personnel available to supervise their operation. Having an optimal remote diagnostic system that can solve most problems without sending a specialized technician is time- and cost-imperative.
OEMs must design automated skids that require a minimum of operator attention and have components and systems amenable to both remote monitoring and remote service. In addition, these systems must have superior mean-time-between-failure metrics because constant operation will place an extraordinary strain on components. This article provides strategies for improving uptime through state-of-the-art control systems.
Accessing electrical diagnostic information
Practitioners of controls engineering are adept at applying decentralized automation platforms that enable a wide variety of functions throughout modern process automation systems. They have learned how to connect and commission a plethora of field devices quickly and economically with the aid of these systems. In addition to integrated pneumatic valve functions, these systems often support the integration of functions such as:
Figure 3: Modern automation platforms make a wide variety of status and diagnostic data available to the user.
It's common for several hundred different devices to be connected to a single remote terminal (see Figure 2).
These systems have been applied in a wide range of applications. The benefits of applying this technology—in terms of installation and labor savings—are well documented and have been embraced by industry. As the sophistication of functions addressed by these systems continues to increase, so does the complexity of installing, commissioning, troubleshooting, and repairing these systems. This effort can be costly and time consuming. Harnessing the power of onboard diagnostic capabilities of these systems dramatically reduces troubleshooting and repair efforts while increasing uptime and productivity.
Modern automation platforms make a wide variety of status and diagnostic data available to the user (see Figure 3). In many cases, the user is not even aware that the automation platform has already done the troubleshooting, and nuisance errors can be reduced by setting parameters for normal operation. For example, setting a signal extension time for a digital input can prevent network latency issues from missing a critical input event that could be shorter than the network scan time (see Table 1).
Table 1: Typical diagnostics
This wealth of diagnostic data is helpful to users only if they can see and act upon it. Depending on the protocol in use (EtherNet/IP, DeviceNet, etc.), diagnostic data can be presented to users of different skill levels in myriad ways (see Table 2).
Table 2: Diagnostic presentation method comparisons
Given the broad matrix of data types and delivery methods, OEMs can customize skids to the data type most appropriate to the application and customer environment. Simple machines that pose low risk to operational capacity can benefit from simple monitoring of status bits, accompanied by an occasional view of the diagnostic memory during a preventive maintenance event. More complex machines that perform critical tasks often benefit from a multifaceted approach to diagnostics. For example:
Using flowmeters as diagnostic tools
Figure 4: Installing a flowmeter at the main air connection will provide volumetric consumption or consumption rate information. This modular assembly also includes a filter, regulator, on/off valve, and pressure and flow sensors.
Compressed air provides the power to open and close process valves on water treatment equipment. It can also be used to scrub the filtration membrane. Compressed air is a measurable resource that has a cost associated with each unit consumed, indicating the health of the automation components. If the filtration skid has an air leak anywhere in the system, it can cause inefficiencies in performance, consume more compressed air, and increase long-term energy costs. In addition, compressed air can point to a failing automation component. A way for operators and OEMs to reduce downtime is to monitor the volume of air being consumed by the system. Monitoring compressed air volume is one of the most important diagnostic tools for skid builders and end users.
It is important to set a baseline while the filtration equipment goes through factory acceptance testing prior to shipment. Installing a flowmeter at the main air connection will provide volumetric consumption or consumption rate information (see Figure 4). With this known variable, consumption can be compared for various cycles or timeframes over the life of the equipment. This information can be accessed via the HMI, can trigger an alarm, and can be accessed remotely over Ethernet.
An increase of air consumption can indicate the following issues:
Detected in advance, these issues can be corrected with a simple proactive service call or maintenance procedure. If the component is left to degrade, the equipment will fail at some point and a more challenging service call is required, and disruption to service is possible.
Proactive service lowers total cost of ownership
Figure 5: Data via Ethernet can be displayed on a local HMI showing an example of air-consumption analysis.
A scheduled proactive service call is more economical and efficient for the user and the filtration equipment OEM. Equipment downtime, urgent field service, and warranty sales calls are often not an ideal scenario for anyone.
Using diagnostic data from the electrical terminal or from the flow sensor can proactively inform the equipment manufacturer about:
This data could be pushed or pulled from the controller over Ethernet or displayed on the local HMI (see Figure 5). Based on this information, a proactive service call or spare parts package could be quickly dispatched to the operator.
When used and included in the control concept from the beginning, the filtration equipment manufacturer can add marketable benefits to help remain competitive:
Many of the diagnostic features noted in this article are included in leading electrical and valve terminals today. The biggest challenge is integrating these features into the control concept in the early design stages to maximize their use.
Close communication between the OEM and water system engineers can determine the operating environment as well as the types of remote monitoring and remote services that will help improve uptime and lower the number of service calls.