As we noted in the last blog, the customer noted that the water pressure varied and the water control valve position did not necessarily represent the flow through the heater. The customer has indicated that they would be able to release some additional funds for process instrumentation.
At this time a flow measurement of the incoming water was added and the control configuration modified and rescaled to respond to actual water flow.
A flow transmitter, FT2, was added and used to replace the valve position feed forward. Since we know the relationship between flow and heating demand we were able to easily rescale the feed forward to steam valve position demand change.
Modifications were made to the configuration, blocks rescaled and system retuned. Customer exercised changes in the upstream water pressure and was again happy with the new configuration results.
Again we received another phone call approximately 3 months later. The customer indicates that when they switch from city water at 70 degrees to well water at 50 degrees, the system takes too long to respond to these changes. They asked if we could help them with the response of the system.
At this time we proposed that we actually measure the incoming water temperature and anticipate the demand to the steam valve. After the customer agrees to the additional costs of the instrumentation, we provide a new solution.
With this modification we no longer depend on the design differential temperature demand for the feed forward, we actually measure the flow and needed increase in water temperature. From these we can directly calculate the power demand and feed forward this scaled demand to the steam valve. Again the system is reconfigured, rescaled and tuned. And again the customer is happy with the changes made to the system. And again we are ready for beer time.
The customer calls back approximately 3 months later and indicates that there are still opportunities to minimize temperature deviations. They have noted that when the other process steam demand changes, the inlet steam pressure changes and they do not necessarily get the steam flow desired into the heater.
Next time – let’s get the steam under control. Hot water project – Phase 4