2. WHAT IS CHEMICAL
DOSING
Chemical conditioning of feed water / steam
condensate cycle, is essential
to prevent corrosion and scale formation
Dosing can be of two types :
H.P. (High Pressure)
L.P. (Low Pressure)
PSI ENGG SYSTEMS P.LTD.
3. WHAT IS CHEMICAL
DOSING
Corrosion:
Corrosive components, especially O2 and CO2 have to be removed,
usually by use of a deaerator.
Remnants can be removed chemically, by use of oxygen scavenger.
Feedwater has to be alkalized to a pH of 9 or higher, to reduce
oxidation and to support the forming of a stable layer of magnetite on
the water-side surface of the boiler, protecting the material underneath
from further corrosion.
This is usually done by dosing alkalies into the feedwater, like sodium
hydroxide (caustic soda) or volatile ammonia.
PSI ENGG SYSTEMS P.LTD.
4. WHAT IS CHEMICAL
DOSING
Treating the boiler feed water
The boiler feed water treatment is normally done with
the following chemicals:
Hardness stabilisers
Deflocculating agents
Corrosion inhibitors
Oxygen binding agents (e.g. hydrazine)
pH value regulation (caustic soda, ammonia)
Defoaming agents
Dosing of these chemicals into the tank of boiler
feed water is done using dosing systems
PSI ENGG SYSTEMS P.LTD.
5. WHAT IS CHEMICAL
DOSING
H.P. DOSING
Corrosion rate of M.S. surface is lowest, when pH is between 9 -
10.
Dosing is therefore done , to maintain pH & reduce scaling
Generally solution dosed into drum under full boiler pressure
PSI ENGG SYSTEMS P.LTD.
6. WHAT IS CHEMICAL
DOSING
L.P. DOSING
Dissolved oxygen in feed water causes serious
corrosion.
Hence "oxygen scavengers" or "de-oxygenators" are
dosed into feedwater.
Dosing done into feed water stream, either at BFP
suction, or at deareator, at low pressures.
Other chemicals may be also added for pH
adjustment of DM water
PSI ENGG SYSTEMS P.LTD.
7. WHAT IS CHEMICAL
DOSING
DOSING CHEMICALS
H.P. DOSING
Phospate solution (combination of di-sodium and tr-sodium
phospate) is generally used, in concentrations from 2.5 % to 7.5 %.
Exact dosage rate depends on pH variation of water in drum.
It prevents scale formation from low remaining levels of hardness
which may have escaped treatment.
Sodium phosphate causes the hardness to precipitate to the bottom
of the boiler where it can be blown down.
PSI ENGG SYSTEMS P.LTD.
8. WHAT IS CHEMICAL
DOSING
DOSING CHEMICALS - L.P. DOSING
Hydrazine Hydrate solution, in concentrations of
about 0.10 % is used for oxygen scavenging
purposes.
Sodium Sulphite solution, is also used as oxygen
scavenger.
Ammonia solution (about 1 - 2 %) is also used, for pH
control of feedwater.
Similarly Morpholine is also used.
Caustic Soda solution is also used, for pH control of
feed water.
Other proprietary chemicals are also available for
same purposes. PSI ENGG SYSTEMS P.LTD.
9. WHAT IS CHEMICAL
DOSING
Further detail on this complicated subject of
water treatment, is available from water
treatment specialists
This is very much a matter for expert advice
and professional analysis .
PSI ENGG SYSTEMS P.LTD.
10. Dosing Systems - Basics
A metering (dosing) pump is required
to deliver a liquid or solution at
specified rate of flow .
The logging and control of flow rates
& total quantity delivered calls for
Dosing Systems (also known as
Chemical Injection Skids).
PSI ENGG SYSTEMS P.LTD.
11. Dosing Systems – Basics -
contd
These skids typically consist of:
Storage tanks or solution preparation
tanks, with
Mixers (agitators)
Level Gauges
Interconnecting Piping
Pipe Fittings
Valves
Instrumentation for flow / pressure
Control Panels/ Control Systems
PSI ENGG SYSTEMS P.LTD.
12. Dosing Systems – Basics -
contd
The total assembly is commonly
referred to as DOSING SYSTEM, or,
Chemical Injection Skid.
A well-designed system should be:
very compact
save space and
be convenient for plant installation as well
as plant operation
Advanced instrumentation features can be
incorporated into the systems, for compete auto-
control & data logging, through plant interface
PSI ENGG SYSTEMS P.LTD.
13. Dosing Systems – Basics -
contd
Considerable design and detailed
engineering efforts are required
for designing individual
components of the skid, and in
integrating the components into
making a compact and efficient
system.
PSI ENGG SYSTEMS P.LTD.
15. Dosing Systems – Usage
Areas
Dosing Skids are used by a wide cross section of
Industry:
Oil and Natural Gas Exploration & Refining
Iron and Steel
Chemicals processing industries
Pulp & Paper manufacture
Thermal Power
Water & Effluent Treatment
Food & Pharmaceutical industries
Personal care products
Machine building Industry
Semiconductor manufacturing
PSI ENGG SYSTEMS P.LTD.
16. Dosing Systems –
Applications
Typical applications include:
Inhibitor Dosing (Cooling water treatment)
Phosphate Dosing/ Hydrazine Dosing (Boiler Feed
Water treatment)
Dye Dosing (Petroleum Industry)
Lubrication of Rolling Mills (Steel Industry)
Reagent Dosing (Pharma industry)
Dosing paper chemicals (Paper Industry)
PSI ENGG SYSTEMS P.LTD.
17. So what exactly is a dosing
system?
First we see some dosing pump
basics……
PSI ENGG SYSTEMS P.LTD.
18. Dosing Pump basics….
The metering pump is a positive displacement
chemical dosing device, with the ability to
vary capacity, manually or automatically, as
process conditions require.
It features a high level of repetitive accuracy
and is capable of pumping a wide range of
chemicals including acids, bases, corrosive or
viscous liquids and slurries.
PSI ENGG SYSTEMS P.LTD.
19. Dosing Pump basics….
Metering pumps are generally used in
applications where one or more of the
following conditions exist:
Low flow rates in ml/hr or LPH are required
High system pressure exists
High accuracy feed rate is demanded
Dosing is controlled by manual control,
computer, microprocessor, DCS, PLC, or flow
proportioning
Corrosive, hazardous, or high temperature
fluids are handled
PSI ENGG SYSTEMS P.LTD.
20. Dosing Pump basics….
There are 2 main types of dosing
pumps:
Plunger Type: The pumping action is
developed by a reciprocating piston which
is in direct contact with the process fluid,
Diaphragm Type: Piston is shielded from
the fluid by a diaphragm. Diaphragms are
actuated by hydraulic fluid between the
piston and the diaphragm.
PSI ENGG SYSTEMS P.LTD.
22. Types of Dosing Pumps
Diaphragm Pump
Plunger Pump
PSI ENGG SYSTEMS P.LTD.
23. Dosing Pump characteristics..
The pumping action is developed by a
reciprocating piston. This reciprocating
motion develops a flow sine wave.
PSI ENGG SYSTEMS P.LTD.
24. Dosing Pump characteristics..
Unlike centrifugal pumps, flow rate is
not greatly affected by changes in
discharge pressure.
PSI ENGG SYSTEMS P.LTD.
25. Dosing Pump Drive
mechanism
The Drive mechanism translates the
rotary motion of the driver into
reciprocating movement. Industrial duty
pumps will submerge this portion of the
pump in an oil bath to assure reliability
during continuous operation.
PSI ENGG SYSTEMS P.LTD.
26. Flow Adjustment
Pump flow rate is adjustable by varying stroke
length
Most metering pumps are supplied with a
micrometer screw adjustment similar to the
one shown here.
The micrometer can also be replaced by an
electronic or pneumatic actuator to adjust
pump flow rate in response to a process
signal.
PSI ENGG SYSTEMS P.LTD.
27. Pump Drivers & Adjustment
The pump is usually driven by an AC
(constant speed) motor.
Flow control (in manual mode) is done
by rotating stroke adjuster knob, which
varies stroke length, from 0 – 100%
Flow control (in auto mode) is done by
use of stepper motor to rotate stroke
adjuster
PSI ENGG SYSTEMS P.LTD.
28. Dosing Pump characteristics..
The metering pump flow vs. Stroke
characteristic curve is linear.
By measuring flow at 2 stroke settings,
plotting both points and drawing a straight
line through them, other flow rates vs. Stroke
can be accurately predicted.
The steady state accuracy of a correctly
installed metering pump is generally +/- 1.0%
or better.
PSI ENGG SYSTEMS P.LTD.
29.
30. Dosing Pump characteristics..
Although a metering pump can generally be
adjusted to pump at any flow rate between 0
and its maximum capacity, its accuracy is
measured over a range determined by the
pump's turndown ratio.
Most metering pumps have a turndown ratio
of 10:1,which simply means that the pump is
within its accuracy rating anywhere between
10% and 100% of capacity.
PSI ENGG SYSTEMS P.LTD.
31. Dosing Pump characteristics..
•Pump stroking speeds can vary from 75
strokes/min to 200 strokes/min
•Higher stroke speeds reduce pump size & give
higher mechanical efficiency
•Lower stroke speeds only serve to increase pump
size and hence cost
•Newer gland packing materials, and improved
designs (such as “floating cross-head”
construction), lead to near-zero wear and
consequent leakage at higher stroking speeds
PSI ENGG SYSTEMS P.LTD.
32. Dosing Pump liquid end..
The liquid end design and materials of
construction are determined by the
service conditions, and the nature of the
fluid to be handled.
Temperature, flow rate, fluid viscosity,
corrosiveness and other factors are
considered
PSI ENGG SYSTEMS P.LTD.
33. Dosing System basics…
In a typical boiler feed water dosing
system:
The HP Dosing system doses direct
into boiler drum, under high pressure.
The LP Dosing system doses into the
boiler feed water pump suction line,
or, de-aerator inlet line, under low
pressure
PSI ENGG SYSTEMS P.LTD.
35. Some boiler installations need 3-pump HP dosing systems, as
shown above. Note the dissolving basket fitted in the dosing tank,
and the top-mounted level switch (to stop pump on low level).
36. The General Arrangement
drawing (known as GA
Drawing) for a typical 2-pump
boiler feed water dosing
system is shown on the next
slide…..
PSI ENGG SYSTEMS P.LTD.
37.
38. Dosing System - Components
Typical components of a dosing
system:
Dosing Pumps
PSI ENGG SYSTEMS P.LTD.
39. Dosing System - Components
Typical components
of a dosing system:
Tanks
PSI ENGG SYSTEMS P.LTD.
40. Dosing System - Components
Typical components
of a dosing system:
Valves
PSI ENGG SYSTEMS P.LTD.
41. Dosing System - Components
Typical components of a dosing
system:
Level gauge for tank
PSI ENGG SYSTEMS P.LTD.
42. Dosing System - Components
Typical components of a dosing
system:
Pressure gauge:
PSI ENGG SYSTEMS P.LTD.
43. Dosing System - Components
Typical components of a dosing
system:
Pressure Relief Valve:
PSI ENGG SYSTEMS P.LTD.
44. Dosing System - Components
Typical components of a dosing
system:
Pulsation dampener
Calibration Column
PSI ENGG SYSTEMS P.LTD.
47. Manual & Auto-Control
Systems
What we have seen till now are manually
operated dosing systems, utilizing standard
mechanical dosing pumps.
These will satisfy the needs of most steady-
state operations
Auto-controlled systems are responsive to
changes in process conditions, requiring
frequent changes in dosing conditions, done
automatically
PSI ENGG SYSTEMS P.LTD.
48. Auto-Controlled Dosing
Auto-control dosing systems need
external logic controllers, which take
signal from process sensors, and adjust
dosing according to pre-determined
values.
PSI ENGG SYSTEMS P.LTD.
49. Standard Controllers used in Auto-Dosing Systems
Conductivity & pH controllers
PSI ENGG SYSTEMS P.LTD.
50. Auto-controlled Dosing
A classic example is a modern
boiler system, where the following
process parameter changes affect
dosing rates:
PSI ENGG SYSTEMS P.LTD.
51. Auto-controlled Dosing - types
Flow-proportional method:
Uses an instrument signal to adjust dosing
rate, based on actual flow of water being
treated
Instrument signal is generated from a flow-
measuring device
Commonly used in boiler plants and
cooling water treatment plants
PSI ENGG SYSTEMS P.LTD.
52. Auto-controlled Dosing - types
Parameter Measurement method:
Measurement of several parameters is
taken from the process
These are analyzed to make the dosing
decisions
Dosing decisions made by the central
processor, based on comparison of
readings with programmed control bands
PSI ENGG SYSTEMS P.LTD.
53. Auto-controlled Dosing - types
Parameter Measurement method:
In a boiler system, parameters such as
dissolved oxygen, pH, and conductivity are
continuously monitored, for dosing
decisions
This method closely monitors multiple
variables, such as flow rate, dissolved
oxygen content, and adjusts dosing rate
accordingly
PSI ENGG SYSTEMS P.LTD.
56. Our Chemical Dosing range
We focus on packaged skid-mounted
dosing systems for cooling water &
boiler feed water treatment.
This is our core business
We have been in this business for over
30 years
A typical system includes metering
pumps, control instrumentation, and all
interconnectingENGG SYSTEMS P.LTD.
PSI pipework.
60. LP Dosing system,
with 2 pumps
local control panel
self-cleaning filters
(16 lph 5 bar)
EPC Contractor:
Alstom Projects India
Ltd.
User:
Bokaro Power
67. IN CONCLUSION….
We focus on high reliability, high
quality, water treatment dosing
equipment
Instead of trying to win your
business by being the cheapest, we
focus on giving you the best
possible equipment that your
budget can bear.
PSI ENGG SYSTEMS P.LTD.
68. THANK YOU
Dosing is an exhaustive subject
We have given a brief overview of
the subject
We will be glad to clarify any
specific queries
We can custom-design systems for
specific applications
PSI ENGG SYSTEMS P.LTD.