MFA pH Controller
Most process plants generate a wastewater effluent that
must be neutralized prior to discharge or reuse. Consequently,
pH control is needed in just about every process plant,
and yet a large percentage of pH loops perform poorly.
Results are inferior product quality, environmental
pollution, and material waste. With ever increasing
pressure to improve plant efficiency and tighter regulations
in environmental protection, effective and continuous
pH control is highly desirable.
A strong-acid-strong-base pH process is highly nonlinear.
The pH value versus the reagent flow has a Logarithmic
relationship. Away from neutrality, the process gain
is relatively small. Near neutrality where pH=7, the
process gain can be a few thousand times higher. There
is no way for a fixed controller like PID to effectively
control this process. In practice, most pH loops are
in a "bang-bang" type of control with pumps
turning on and off resulting in large oscillations.
Since acid and caustic neutralize each other, over-dosing
acid and caustic is prohibitively expensive. Statistics
show that a poorly controlled pH process can cost tens
of thousands of dollars in chemical usage each month
not counting the penalties imposed by violating EPA
or local government discharge code.
The MFA pH controller can effectively control a wide
range of pH processes within the full pH range. It is
useful for wastewater neutralization and also enables
automatic control of acid or alkaline concentration,
both of which are critical quality variables for the
chemical process industry.
MFA pH Controller Configuration
As shown in the following graph, one can easily enter
Break Point A and B to define the estimated shape of
the titration curve of the pH process. Then the MFA
controller gain Kc for the flat portion and steep slope
can be entered. For a strong-acid-strong-base pH process,
if the controller gain for the flat portion is 1, then
the gain for the steep slope can be estimated as 0.001,
which is 1000 times smaller. Due to the adaptive capability
of the MFA controller, the titration curve does not
have to be accurate. In fact, its shape can vary in
real applications. In addition, the flow rate and the
pH value of the inflows may vary significantly. The
MFA pH controller can effectively deal with these large
disturbances.
MFA pH controller configuration menu
The MFA pH controller has helped many users effectively
control their tough pH loops. Payback in weeks or even
days has been reported with savings on chemical reagents,
avoiding violation of discharge codes, and smoother
production operations.
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