AUTOFLAME Mk8 MM User Manual

16 Heat Flow
Mk8 MM Manual Page | 282
Example 2: Steam with Deaerator
A common practice in steam generation is the use of a “deaerator” to remove the oxygen from the feed water
and hence reduce the incidence of oxygen corrosion in the boiler and steam & condensate pipework.
The principle of a deaerator is to mix the make-up water with the condensate return and live steam direct
from the boiler in a tank. Flash steam may also be directed back to the tank. The effect is to mechanically
“scrub” the oxygen from the feed water and also to preheat it before it is pumped into the boiler.
In the system as set out above, it is no longer valid to measure the temperature of the feed water just before
it enters the boiler as the inlet temperature for the “steam meter” calculation. This water has already been
preheated by steam from the boiler and therefore this additional energy should not be taken into the software
calculation.
The solution is to treat the boiler and deaerator as one system. The energy into the system is supplied by the
burner and the inlet temperature is the “weighted average” of the condensate return temperature and
makeup water temperature. The outlet steam temperature is measured by a temperature sensor in exactly
the same way as in a system without a deaerator.
First the percentage “Make up“ in the “Feed water” must be calculated.
%Mu =
100 x V2
(V2 + V1)
Where:
%Mu
=
% Cold make up water
V1
=
Volume flow rate of condensate return water
V2
=
Volume flow rate of cold make up water
Assuming a steam boiler with a volume of condensate return of 40 GPM and make up water of 8 GPM;
Make up % =
100 x 8
(8 + 40)
= 16.7%
In order to calculate the second part to establish the “Weighted Average Temperature”, the following
equation is used.
Tave = T3 
(%Mu x (T1A  T1))
100
Where:
T
ave
=
Weighted Average temperature
T3
=
Temperature of condensate
T1
=
Temperature of make up water
%Mu
=
Percentage of make up water
Steam boiler with condensate return temperature of 176°F and a make up water temperature of 41°F. From
the above example the make up percentage is 16.7%
Weighted Average = 176 
(16.7 x (176 – 41))
100
= 153.4°F
To implement the above control, the above calculations have been imbedded in the MM to obtain the
“Weighted Average Temperature” (T
ave
).

AUTOFLAME Mk8 MM Specifications

General

Brand	AUTOFLAME
Model	Mk8 MM
Category	Controller
Language	English