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MIL-D-16196E(SH)
(c) Compressed vapor saturation temperature not to exceed 250F.
(d) Temperature of distillate from the unit not to exceed 125F unless
otherwise specified (see 6.2).
(e) Concentration ratio not to exceed 1.8. Concentration ratio is
defined as (feed flow rate) divided by (feed flow rate minus
distillate rate).
(f) Quality of distillate in accordance with 3.4.3.
3,4,2 Scale control.
The distiller design shall include provisions for
on-line injection of feedwater chemicals to control scale formation and for
off-line injection and circulation of NAVSEA approved acid solutions to remove
On-line is defined
built up scale which cannot be controlled by on-line methods.
as not interrupting the production of distillate, that is, the distiller
continues to make rated capacity and quality as defined in 3.4:  Off-line is
defined as corrective maintenance performed when the distiller is not being
operated to produce distillate,
3.4.2.1 On-line injec tion of feed treatment chemicals to control scale
formation.
The On-line chemical feed treatment process shall not interfere with
or reduce the rated capacity of the distiller,
For class A units, the process
may use either the continuous injection feed treatment system (see 3.4.2.1.2) or
Class B, type II units shall use
the Periodic acid shot method (see 3.4.2.1.1).
the continuous injection system.
The PAS system
3,4.2.1.1 Periodic acid shot (PAS) feed treatment system.
provides for injection of an acid solution into the distilling plant seawater
Each acid shot remove scale
circuit at approximately 6 to 8 hour intervals.
built up since the last injection.
The acid solution shall be sodium bisulfate
(see 6.10).
The continuous
3,4.1.2 Continuous injection feed treatment system.
injection feed treatment system provides continuous injection of NAVSEA approved
This system shall also
feed treatment chemicals to retard scale formation.
provide for on-line injection of citric acid in accordance MIL-C-11029 to remove
the sludge type scale formed by continuous injection of approved feed treatment
chemicals .
Continuous injection of acid solutions to control scale is prohibited
(see 6.10).  The use of sulfamic acid for on-line cleaning is prohibited whenever
the distiller process temperatures exceed 150F.
3.4.2.2  Off-lin e acid cle aning.
In order to remove the scale that forms
despite use of on-line treatment methods,  the distiller design shall include
The acid solutions shall be
provisions to inject and circulate acid solutions.
sulfamic acid with corrosion inhibiters (see 6.10).
The acid solution shall be
circulated through the evaporator, brine pump,  feed heat exchangers and all other
A method shall
components and piping which are susceptible to scale formation.
also be provided to heat the acid solution to a temperature of 120F to increase
acid reaction with the scale,
Boiler section heaters may be used for this
purpose.
Since this is an off-line maintenance requirement, cross connecting
piping and acid storage tanks and so forth, necessary to accomplish this function
Rather, adequate provision shall be
shall not be included with the distiller.
made to provide connections, fittings, and so forth so that a maintenance
activity may easily set Up the distiller for off-line cleaning.
11

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