Neometrix / Process Skids / Chemical Dosing System / NMX-DSK-85

NMX-DSK-85 · ENGINEERED-TO-ORDER CLASS — SPECIFY · SELECT · PACE · INJECT · CONTAIN · PROVE

Chemical Dosing System. Flow sets it; the residual trims it.

Name: Chemical Dosing System
Brand: Neometrix
SKU: NMX-DSK-85

A chemical dosing system puts a treatment chemical into a process stream at the rate the stream needs: an oxidant or scavenger for a water-steam cycle, a biocide or inhibitor for cooling water, a neutralising agent, an odorant for a gas line. Neometrix engineers it as a metering-pump skid: a day vessel, duplex pumps, a calibration column, pulsation damping, back-pressure and relief protection, a flow meter and an injection point.

So the system has to pace the dose to the flow, trim it to the residual, and contain what it handles.

Discuss a chemical dosing system Capability note (PDF)

A chemical dosing skid on a plain white studio background: a pale grey steel base frame with a shallow stainless drip tray, a tall plain off-white polyethylene day vessel with a round lid at the back, two identical metering pumps with bright stainless pump heads and finned motors side by side at the front, a clear glass calibration column beside them, two small bright steel vessels and a bright flow meter and back-pressure valve on the discharge side, joined by neat stainless tubing, and no people

Fig · 01 — A chemical dosing skid: a day vessel, duplex metering pumps, a calibration column and the discharge fittings on one frame, in a drip tray — illustrative render.

The result

a dose that follows the streamand a record of what was delivered

The pace

set by the process flowfeed-forward, acting at once

The trim

from the measured residualslow, with no derivative action

The pumps

duty and standbyoutput proved on a calibration column

Status

engineered to orderno delivered skid claimed

ISO 9001ISO 14001API 675 reference standard

Overview

Why the pump is the easy part, and the control is where the dose is won.

Because a metering pump delivers what it is told, and the hard part is telling it the right amount at the right time, for a process that never stands still.

A duplex metering pump set on a plain white studio background: two identical metering pumps side by side on one pale grey base plate, each with a bright stainless pump head with a domed cover and a finned electric motor behind it, a bright stainless suction manifold along the front with a clear glass calibration column at its left end, a bright discharge manifold along the top with a small bright steel vessel on each discharge branch, and one outlet tube leaving to the right, and no people

Fig · 02 — A duplex metering pump set: two identical pumps, a suction manifold with a calibration column, and a discharge manifold with a dampener on each branch — illustrative render.

Flow sets the dose; the residual trims it.

What the system is for

It puts a prepared treatment chemical into a process stream: an oxidant, a scavenger, a biocide, a corrosion inhibitor, a dispersant, a neutralising agent or an odorant. It does the job continuously, at a rate that follows the stream, and it keeps a record of what it delivered.

Why the dose is paced to the flow

A stream does not run at one rate. A pump that runs at one rate gives a concentration that rises when the flow falls and falls when the flow rises. So the controller takes the flow signal and sets the pump's output in proportion to it. That is feed-forward, and it acts at once.

Why the dose is trimmed to the residual

The flow does not show what the stream uses up. An analyser downstream reads the residual of the chemical and moves the ratio up or down. Its reading arrives late: the stream has to travel to it, and the sample line delays it again. So the trim is slow, carries no derivative action and is held to a band around the flow-proportional dose. A fast trim on a late reading does not correct the dose; it chases it.

Why the pump has to be proved

A metering pump's output depends on its stroke, its speed, its suction conditions and the pressure it works against. A calibration column on the suction side lets the output be measured against a volume of liquid instead of assumed. Used on a schedule, it shows wear before the dose drifts.

Why the pulsation and the back-pressure matter

A positive displacement pump delivers in pulses. A dampener on the discharge smooths them, so that the flow meter and the process see a steady flow. A back-pressure valve keeps a steady pressure on the pump, and a relief valve that returns to the vessel protects the line.

Why the containment is part of the design

The chemical is the hazard. The skid stands in a bunded drip tray, the wetted parts are chosen for the chemical, and chemicals that must not meet are kept apart.

The method

Specify, select, pace, inject, contain, and prove.

Six steps in a fixed order. The pacing and the injection are the two that a quick order skips.

1 · Specify

The chemical and its strength, the stream and the range of its flow, the point of use, the analyser and the site are stated by the customer.

2 · Select

Controlled-volume metering pumps of the type the chemical suits, wetted parts that agree with it, and a vessel, strainer, valves and pipework of the same material.

3 · Pace

A flow signal sets the pump's output in proportion, and a slow trim from the residual moves the ratio inside a limited band.

4 · Inject

An injection fitting with a check valve puts the chemical into the stream ahead of a mixing section. The sample point sits after it, far enough for the chemical to have mixed.

5 · Contain

A drip tray under the skid, a level signal and a vent on the vessel, a relief path that returns to it, and interlocks that stop the pumps when something is wrong.

6 · Prove

Each pump is checked on the calibration column, the loop is tried on water, the interlocks are exercised, and the record is handed over with the skid.

Which dosing, which job

Scheme	How it sets the dose	What to watch
Fixed-rate dosing	the pump is set once and left	the stream varies, so the concentration varies with it
Flow-proportional dosing	the pump follows a flow signal	it ignores what the stream uses up, so a change in demand goes uncorrected
Flow-proportional with residual trim (this page)	the pump follows the flow, and a slow trim moves the ratio from the residual	where the sample point sits, and how late its reading arrives
Residual-only feedback	the pump follows the analyser alone	a long delay makes it overdose, wait and underdose in turn
Batch dosing	a measured volume is added for each volume of stream passed	the pump is idle between doses, and the mixing has to catch up

The step people underrate is the slowness of the trim. A fast loop on a late reading makes a steady stream look unstable, and an unstable one look steady.

Work content

What the system contains, element by element.

Read it as a checklist: a skid missing a row will pump a chemical, but not one you can set a dose with and trust it.

A short run of process pipe with its dosing connections on a plain white studio background: a straight horizontal bright stainless pipe with a bolted flange at each end on two pale grey saddle supports, a small bright injection fitting entering the top near the left end through a ball valve with a thin tube rising from it, a plain bright cylindrical mixing section in the middle, and a small bright sample connection with a ball valve and a short tube nearer the right end, and no people

Fig · 03 — The injection and the sample point: a fitting that puts the chemical into the stream, a mixing section, and a sample connection further along — illustrative render.

Element	What it does	What matters
Day vessel	holds the chemical	made of a material that agrees with the chemical, with a level signal, a vent and a drain
Suction line and strainer	feed the pumps	short and flooded where it can be, with a strainer that can be cleaned without stopping the duty pump
Calibration column	measures the pump's output	on the suction side, clear, with its own isolating valves, and used on a schedule
Duplex metering pumps	deliver the dose	controlled-volume pumps of the diaphragm or plunger type, each able to carry the full duty, one on duty and one standing by
Pulsation dampener	smooths the pulses	on the discharge, sized to the pump, so that the flow meter sees a steady flow
Back-pressure and relief valves	protect the pump and the line	a steady pressure against the pump, and a relief path that returns to the vessel
Flow meter on the dose line	reads what the pump delivers	closes the loop on the pump itself, so a worn pump shows at once
Injection fitting and mixing section	put the chemical into the stream	a fitting with a check valve, ahead of a mixing section that gives the chemical a distance to blend
Sample point and analyser	read the residual	placed after the mixing, with the delay of the sample line known and allowed for
Controls	pace, trim and protect	a flow-proportional ratio, a limited slow trim, duty and standby changeover, alarms and interlocks
Drip tray and containment	hold what leaks	a tray under the skid, wetted parts chosen for the chemical, and chemicals that must not meet kept apart
Procedure	fixes the sequence	specify, select, pace, inject, contain and prove, the same for every skid
Testing & documentation	prove the skid first	each pump checked on the column, the loop tried on water, the interlocks exercised, and a record the customer can inspect

The elements that decide the dose are the pacing logic and the injection and sample arrangement, and the one that decides whether it stays right is the calibration column. The first two set the dose, and the third keeps the pump honest.

Full specification — expand

System	A day vessel with a level signal, a vent and a drain; a suction line with a strainer; duplex controlled-volume metering pumps, duty and standby, of the diaphragm or plunger type chosen for the chemical; a calibration column on the suction side; a pulsation dampener on the discharge; a back-pressure valve and a relief valve that returns to the vessel; a flow meter on the dose line; an injection fitting with a check valve ahead of a mixing section; a sample point and a residual analyser; controls that pace, trim, limit and change over; a bunded drip tray; a written procedure; and testing and documentation before handover
The One Idea	Flow sets the dose; the residual trims it.
Why The Dose Is Paced To The Flow	A stream does not run at one rate, so a pump at one rate gives a concentration that rises when the flow falls and falls when the flow rises, and the controller therefore takes the flow signal and sets the pump's output in proportion to it, which acts at once
Why The Trim Is Slow	The chemical is used up by what is in the stream, which the flow does not show, so an analyser downstream reads the residual and moves the ratio; its reading arrives late, after the stream has travelled and the sample line has delayed it, so the trim is slow, carries no derivative action and is held to a band around the flow-proportional dose
Why The Pump Is Proved	A metering pump's output depends on its stroke, its speed, its suction conditions and the pressure it works against, so a calibration column on the suction side measures the output against a volume of liquid instead of assuming it, and a check on a schedule shows wear before the dose drifts
Standards	API 675 covers controlled-volume positive displacement pumps for petroleum, chemical and gas industry services. This page prints none of their limits, classes or tolerances, and no edition year: those come from the standard the customer names and from the pump maker. Approval of a pump, a skid or a dose rests with the customer and the authority they name; none is claimed here
Configurations	A water-cycle dosing skid, a cooling and process water dosing skid, and a line injection skid
Scope Boundary	This page is the chemical dosing system, which doses a prepared chemical into a process stream. It is not a foam proportioning system, which mixes foam concentrate into a fire water stream (see foam proportioning system), not a gas mixing system, which blends gases to a set composition (see gas mixing system) and not an instrument calibration bench, which calibrates instruments (see instrument calibration bench). It does not make a chemical on site, and it is not a bulk chemical store. No certification or accreditation is claimed here
Status	Neometrix has quoted against successive chemical dosing system requirements, and no delivered chemical dosing system is claimed.

Configurations

One method, three ways to build the skid.

The method, the pump check, the pacing logic, the injection arrangement and the procedure are shared. What changes is the stream, the chemical and whether there is an analyser to trim from.

Water-cycle dosing skid

A conditioning chemical paced to the feedwater and trimmed from its analyser

For an oxidant, a scavenger or a conditioning chemical in a water-steam cycle, paced to the flow of the water and trimmed from a residual analyser, with duplex pumps so that the dose never stops.

Cooling and process water dosing skid

A biocide, an inhibitor or a dispersant paced to make-up and blow-down

For several chemicals into one circuit, each with its own pump pair and calibration column, paced to the flows that change the circuit's demand and kept apart where they must not meet.

Line injection skid

An additive or an odorant paced to the flow in a line, with no analyser

For a line where the dose follows the flow alone, with a quill into the line, a check valve, and a column that proves the pump on a schedule instead of an analyser that trims it.

And the part that is not equipment at all, yet decides all three: the procedure and the test plan. They fix the chemical, the flow signal, the limits on the trim, the checks on the pump, the order they run in and what is recorded. They are written from the customer's own stream and chemical, not from the skid.

The drawing

A reference sheet, drawn as a real CAD sheet.

One sheet of one reference configuration: the process and instrument schematic of a dosing skid. It shows how the dose is paced and trimmed, how the pumps are proved, and what the skid does when something goes wrong. It carries tags and arrangement only. Every flow, pressure, concentration and time is fixed by design for the customer's stream and chemical.

Reference drawing sheet, the process and instrument schematic of a chemical dosing skid. A day vessel with a level transmitter, a low-level switch and a vent feeds a suction header with a hand valve and a strainer, and a calibration column branches off the header through an isolating valve. Two identical metering pumps, each with its own motor and suction valve, push through pulsation dampeners into a discharge header with a pressure switch, a relief valve that returns to the vessel, a back-pressure valve and a flow meter. The dose line leaves the skid through a check valve and enters a process line at an injection fitting, ahead of a mixing section and a sample point with a residual analyser. A flow transmitter on the process line and the analyser send signals to a dosing controller, which commands the pumps. A bund level switch, a legend, a table of trips and alarms, eleven notes and a title block stamped reference configuration, not for construction

Fig · 04 — Sheet 01, the process and instrument schematic: the metering pumps, the calibration column, the injection, and the two signals that set the dose. Reference configuration, tags only.

Every real skid is drawn for its own chemical, stream and site. This sheet is the arrangement and the order of control that a project set starts from. Approval of any drawing rests with the customer and the authority they name; none is claimed here.

PDF · one sheet

Reference drawing — process and instrument schematic

PDF · capability sheet

Chemical dosing system — what Neometrix engineers

Where it is used

Wherever a chemical is added to a stream, and the stream will not hold still.

The common thread is a flow that varies, a chemical that is used up, and a dose that has to be right without anyone standing beside it.

Power plants

Where the water-steam cycle is conditioned and the cooling water is treated, and a wrong dose shows up as corrosion or fouling.

Cooling-water circuits

Where biocides, inhibitors and dispersants go in at rates that follow make-up and blow-down.

Refineries and process plants

Where inhibitors and additives are injected into lines and units, and the pump has to be proved rather than trusted.

Gas and fuel handling sites

Where an odorant or an additive is injected in proportion to the flow in a line.

Watch

See it in motion.

A short walkthrough video of the chemical dosing system.

FAQ

Common questions.

Longer answers, for readers who want the reasoning.

Q · 01 What does a chemical dosing system actually do?

It puts a prepared treatment chemical into a process stream at a rate that follows the stream. The controller takes a flow signal and sets the output of a metering pump in proportion to it, a slow trim from a residual analyser moves the ratio, and a flow meter on the dose line shows what the pump delivered. It does not decide what dose the process needs: that comes from the customer's water chemistry or process, and the system holds it.

Q · 02 Why pace to the flow and trim to the residual, and not just use one?

Each one alone fails in a different way. Pacing to the flow alone acts at once, but it cannot see what the stream uses up, so a change in demand goes uncorrected. Steering on the residual alone sees the demand, but its reading arrives late, because the stream has to travel to the analyser and the sample line delays it again, and a loop on a late reading overdoses, waits and then underdoses. Together, the flow sets the dose at once and a slow trim, held to a band, corrects for demand. The trim carries no derivative action, because the delay in the loop is long.

Q · 03 Why a calibration column?

Because a metering pump's output depends on its stroke, its speed, its suction conditions and the pressure it works against, and the only way to know what it delivers is to measure it. A calibration column on the suction side lets the pump draw a known volume of liquid, so the output is measured instead of assumed. Used on a schedule, it shows a worn diaphragm or a leaking valve before the dose drifts, and it checks the flow meter on the dose line at the same time. It sits on the suction side so that the pump draws from it in the usual way.

Q · 04 Why two pumps, a dampener and a back-pressure valve?

Two pumps, each able to carry the whole duty, let one stand by, so the dose does not stop when a pump is serviced or fails. A positive displacement pump delivers in pulses, and a dampener on the discharge smooths them, so that the flow meter and the process see a steady flow. A back-pressure valve keeps a steady pressure on the pump, which also stops the chemical being drawn through it when the line pressure is low. A relief valve that returns to the vessel protects the line if something closes. None of these is exotic. A skid that leaves any of them out will pump, but it will not dose well.

Q · 05 Is this the same as the foam proportioning system, the gas mixing system or the instrument calibration bench?

No, and the differences are worth stating precisely. The foam proportioning system page covers mixing foam concentrate into a fire water stream. The gas mixing system page covers blending gases to a set composition. The instrument calibration bench page covers calibrating instruments, the kind this system's flow meters and analysers rely on. This page is the chemical dosing system, for a prepared treatment chemical added to a process stream. It does not replace any of them, and it does not claim what they claim a second time.

Q · 06 Has Neometrix built one of these?

We would rather answer this plainly than let a page imply otherwise. Neometrix has quoted against successive chemical dosing system requirements, and no delivered chemical dosing system is claimed. What stands behind the offer is adjacent: Neometrix engineers a foam proportioning system (see the foam proportioning system page), a gas mixing system (see the gas mixing system page) and an instrument calibration bench (see the instrument calibration bench page). The metering pumps, flow meters, analysers, valves and logic controllers are catalogue items, bought in, not invented. What Neometrix engineers is the skid around them: the vessel and pipework, the pump check, the injection and sample arrangement, the controls, the procedure and the record. So the honest position is that the system is engineered to order, the neighbouring disciplines are in the building, and the first system of this exact kind will be built around the customer's own stream and chemical rather than taken off a shelf.

Q · 07 Which standard applies, and what can the system not do?

API 675 covers controlled-volume positive displacement pumps for petroleum, chemical and gas industry services. This page prints none of their limits, classes or tolerances, and no edition year: those come from the standard the customer names and from the pump maker. The system doses a prepared chemical and keeps a record. It does not make a chemical on site, it is not a bulk chemical store, and it does not decide the right dose for a process: this page claims no certification or accreditation. No flow, pressure, concentration, time, size or quantity figure is printed here, and approval for use rests with the customer and the authority they name; none is claimed here.

Q · 08 What do you need from us to quote?

Six things, and most of them describe your stream rather than the skid. First, the chemical: what it is, its strength and what it must not meet. Second, the stream: the range of its flow and how fast the flow changes. Third, the dose: the range you need, and whether the demand changes. Fourth, the analyser: whether there is one, where it sits and how far the sample has to travel. Fifth, the site: the floor, the supply, and how the chemical is delivered. Sixth, the record: what you want kept. From that we come back with a skid concept, a written test plan you can check, and a budgetary price.

The neighbouring pages, and how they differ from this one.

Three neighbours: one mixes foam, one blends gases, one calibrates instruments.

↗ Foam

Foam Proportioning System

Mixes foam concentrate into a fire water stream - a proportioner for a firefighting duty, where this page doses a treatment chemical into a process stream.

↗ Gases

Gas Mixing System

Sets the flows and proves the mix of gases - a blend to a composition, where this page paces a liquid dose to a flow.

↗ Calibration

Instrument Calibration Bench

Calibrates instruments against a reference - the kind of bench the flow meters and analysers on this page rely on.

Browse all Neometrix product lines.

Get a quotation

Tell us the chemical,
and the stream it goes into.

The projects desk replies within two working days with a skid concept, a written test plan you can check, and a budgetary quotation. Write to [email protected] or use the form.

Enquire — chemical dosing system Capability sheet (PDF) +91 7777 876 876

ISO 9001 / 14001 ENGINEERED-TO-ORDER CLASS — CHEMICAL DOSING SYSTEM SPECIFY · SELECT · PACE · INJECT · CONTAIN · PROVE — FLOW SETS THE DOSE; THE RESIDUAL TRIMS IT ENGINEERED IN NOIDA · INDIA