The last project I did on just such a system consisted of a tank, heat exchanger recirc pump for heating and a pump to feed 95 Deg. C water to a cooker, the cooker was an in-line system that cooked rice (first in the world I believe it was even sold to the Chinese). The water was sprayed via 6 zones using a mark/space ratio depending on the speed & hence the feed ratio of the dry product, the screw feeder also agitated the product on a forward/back ratio. the original hot water supply struggled to maintain temperature as well as pressure so in effect caused variations in water takeup of the product. The valves were zoned so it was possible to have just some or even all valves open at the same time & as a consequence caused major pressure variations. We added a PID controller to try to compensate for the pressure increases/drops but no matter how we tried it we could not get the control we required. We then designed a new system with a larger capacity tank standby/duty pumps (made maintenance easier whithout shutdowns etc. We called in an expert for the design of the heat exchanger pack based on our requirement and although they were not involved in the pressure control of the feed water the company suggested from their vast experience to ditch the PID controller and use the reverse acting pressure reducing valve in the return line. This proved to be the best choice, no need to set up complicated PID settings, purely mechanical (well hydraulic) low maintenance and fast.
Sometimes the simplest is the best. looking at the pressure log showed almost a strait line but bearing in mind the logging frequency and the filter we added to the log.
Sometimes the simplest is the best. looking at the pressure log showed almost a strait line but bearing in mind the logging frequency and the filter we added to the log.