BENEFITS OF AUTOMATING THE APPLICATION OF KNOWLEDGE IN THE BPCS
For years many companies in the oil, gas and chemical industries have been dealing with the loss of their most experienced operators to retirement. Recent developments have accelerated the loss of engineers and operators along with the institutional knowledge that they carry. This is an area where additional automation can be beneficial to help make up for knowledge and experience that otherwise would be lost.
ALARM RESPONSE PROCEDURES
When an alarm activates, the operator needs to troubleshoot what is happening in the process and determine an appropriate response. Traditionally, this is done by referencing a written procedure or relying on the operator’s knowledge. One automation tool that’s available to make this more efficient is the use of alarm response procedures, commonly called “alarm help,” within the BPCS, which can be a way to immediately inform the operator of the most likely problems and their solutions. This enables the operator to troubleshoot and respond more promptly and effectively.
AUTOMATED RESPONSE TO AN ABNORMAL SITUATION
Taking this concept a step further, if a certain alarm or process condition is always addressed using the same solution, then the response procedure could potentially be automated. Rather than waiting for the operator to work through the alarm response procedure, the BPCS can immediately take a corrective action to override or constrain the actions taken by its controllers, return the process to its normal limits or move to a safer mode of operation.
For example, if the response to a high-pressure condition is to reduce the flow rate of steam to a heat exchanger, the BPCS can take this action on its own and inform the operator of what it did. The role of the operator then becomes verification that the action taken was sufficient to resolve the upset condition or make further adjustments if needed.
These types of automated responses can be particularly valuable if there is insufficient response time available for the operator to be able to reliably take corrective action. Because the automated response is most likely in the BPCS, it may or may not be able to be credited with any additional RRF. But because it can act more promptly and consistently than a human, it still can be effective at maintaining stable operation and avoiding an SIS shutdown that might otherwise occur.
Some alarms are only meaningful when the associated equipment is in a certain operating state. For example, if a pump is not intended to be running, then the low flow or low pressure alarm located in the pump discharge is not necessarily useful and could in fact become a nuisance and ignored over time. This is not the case if the pump was intended to be running and the alarm has purpose. A BPCS that keeps track of the intended and actual operating states of equipment can be programmed to shelve alarms that are not relevant at that time.
Not every alarm has a simple response. Some upset conditions are highly complex and require the operator to review the status of multiple variables to understand what’s happening and determine the appropriate response. There is an automation solution for this as well. Multivariable alarms can evaluate the values and trends of several variables simultaneously and present the most likely problem and solution to the operator for implementation.
An example is if there is insufficient oxygen available to completely combust the fuel in a fired heater. The correct response for the operator to take may be dependent on whether it is taken early when the products of incomplete combustion have just started to appear in the flue gas, or later, after a significant volume of combustible material has already accumulated in the firebox.
A multivariable alarm can evaluate variables such as the oxygen and/or combustibles content of the flue gas, process temperatures, and fuel gas flow rate to determine what’s happening and suggest the correct response. Equally important, the alarm can suggest responses to avoid, such as not changing air flow in response to a low oxygen alarm.
The correct response generally is to slowly decrease fuel flow until the oxygen in the flue gas recovers. An experienced operator will likely know this. A newer operator may take the incorrect, but instinctive, action to add more air when the oxygen goes low, which could result in an explosion of the accumulated fuel.