Base level control via feed

Base-Level Control via Feed-Flow Manipulation... 

Bottom-Product Demand Base-Level Control Via Feed... 

Bottom product demand, overhead level control via reflux, base level control via feed... 

In a recent project we had considerable difficulty with base level control via feed accompanied by steam/feed ratio control. In effect the level controller adjusts both feed and steam. Since bottom produrt was the demand flow, this was corrected by converting the steam/feed ratio control to steam/bottom-product ratio control. 

COLUMN-BASE LEVEL CONTROL VIA FEED FLOW... 

Signal flow diagram for proportional-oniy column base level control via feed flow manipulation... 

If the bottom product is the demand stream, then base level control via boilup and reflux drum level control via distillate will not control the column properly. An increase in bottom product will cause a decrease in distillate, with no change in feed rate. 

As indicated earlier, reflux drum level control via boilup is difficult unless a lot of holdup is available. Overhead composition may be controlled by trimming the reflux/distillate ratio base composition may be controlled by trimming the bottom-product/distillate ratio. Note that if either distillate or bottom product (or side product) is a demand flow, either reflux drum or base level control must manipulate feed rate. 

However, many differences arise among the schemes when looking at how production rate is set and how liquid level and pressure in the reactor are controlled. For example, production rate is set in various strategies via fresh feed Fo0 flow, condenser cooling water flow, separator liquid flow, stripper base flow, or fresh feed FoC flow. Reactor level is controlled by fresh feeds FoD and F,lK, separator temperature setpoint, compressor recycle valve, or fresh feed FoC flow. Reactor pressure is controlled by reactor cooling water flow, purge flow, or FcA feed flow. In one strategy reactor pressure is uncontrolled and allowed to float. 

Traditionally, a common solution to the problem of matching relatively higher levels of technical support with lower chemical volumes for these smaller customers has been via a one- to three-year, fully inclusive product and services contract. Such a contract will specify the frequency of service visits to be made to the customer s site and the type of work to be carried out. It will also, perhaps, limit the maximum volumes of chemical treatments to be supplied during the contract lifetime, or perhaps designate the amount of chemicals required based on treating a certain annual volume of boiler FW. Contracts may include for the provision of chemical feed and control equipment and for the supply of labor for boiler cleaning, chemical addition, and drum removal services (drumless delivery). Product and services contract prices may some-... 

The general operation of the pilot scale reactor has be previously described by Pareek et. al. [3]. However, modifications were required to allow the injection of the gas and liquid tracers, and their subsequent detection at the outlets. The liquid tracer, 5mL Methyl blue solution (lOgL" ), was injected via a syringe inserted into the liquid feed line. Outlet samples were measured with a Shimadzu 1601 UV-Vis Spectrophotometer at a wavelength of 635nm. A pulse (20mL) of helium gas tracer was introduced using an automated control system, with the outlet concentration monitored in real-time with a thermal conductivity detector. Runs were carried out based on a two-level... 

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