How to Specify a Demister RFQ

A clear RFQ can shorten engineering review and reduce the risk of a wrong construction. You do not need a perfect datasheet. You need the fields that change the design — and you need to say which kind of enquiry you are making, because that defines what conformity means for the offer.

First, say which enquiry route you are on

Most demister enquiries can be controlled through one of four routes. They demand different data and allocate responsibility differently; if the route is unclear, competing quotations may be based on different obligations.

Catalogue or standard item. You know the construction you want and only need price, availability and delivery. Send the specification you already have. The supplier’s obligation is to match that specification — not to validate that it suits your process.

Build to drawing. You have a controlled drawing or a complete parameter set and want it manufactured. The order should require conformity to that basis, including specified material and tolerances. Unless you separately agree otherwise in writing, it does not include a guarantee that the design will achieve a separation performance. A conforming part cannot correct an error in the buyer-provided design basis.

Performance guaranteed. You want the supplier to warrant a separation result — an efficiency at a stated droplet size, or an outlet loading. This requires the full duty envelope and acceptance method to be frozen, including applicable upset cases, and normally requires more engineering review and risk pricing than build-to-drawing supply.

Replacement without a drawing. You have a vessel, an old pad and no reliable documentation. The manufacturing basis has to be controlled from physical evidence; see mist eliminator replacement without drawings for the evidence set and the pitfalls.

State the route at the top of the enquiry so that suppliers price the same responsibility.

Process data that actually changes the design

Gas flow — at actual conditions

Volumetric flow at operating temperature and pressure is needed to size the flow area. If you only have a mass flow or a “normal” volumetric flow, send it together with temperature, pressure and composition so it can be converted, and state the reference conditions used for “normal.” Treating normal-condition volume as actual-condition volume can create a large sizing error, especially when pressure differs substantially from the reference basis.

Vapour and liquid density

These enter the Souders–Brown velocity used for first-pass sizing. If you have values from a process simulation, send them with their operating basis; otherwise composition-based estimates must state their assumptions. The demister sizing calculator on this site shows how the terms combine, and what a K-factor derate does to required area.

Send the actual operating pressure with them. The allowable K value is a preliminary engineering input, not a universal constant or a performance guarantee. Pressure, foaming, liquid load, mesh style, disengagement geometry and required margin can all require a case-specific value; glycol contactors are discussed in glycol contactor demisters.

Temperature and pressure, including upset

State normal, design and credible upset values separately. Temperature, exposure time and sustained load can control polymer suitability, while pressure affects vapour density and actual volumetric flow. A single “operating temperature” number does not define the required thermal envelope.

Chemistry — including the trace components

Send the available stream composition rather than only a service name. “Sour gas”, “scrubber”, “acid” and “brine” are categories, not chemistry. Chlorides, HF, strong acids, caustics, oxidants and trace contaminants can redirect material selection. Include water content and known contamination history, and see demister pad materials selection.

Liquid load and solids

Litres per unit of gas, or at least an order of magnitude, plus whether solids are present. In fouling service, increasing mesh density can be counterproductive, and a vane pack may be a better candidate when the required droplet removal and available space allow it; see demister fouling and clogging and mesh pad vs vane pack.

Droplet size and target — only if you need performance

If you want an efficiency figure to mean anything, it must be tied to a droplet size basis and an operating point. An unqualified “99% efficient” is not a specification. If you have a target outlet loading or an emission limit, state it, along with the allowable pressure drop.

Vessel geometry and installation constraints

• Vessel inside diameter at the demister elevation.
• Manway clear opening — this caps section size and therefore the whole segmentation design.
• Support ring dimensions and elevation, or a note that none exists yet.
• Available height above the support ring, which caps total thickness including grids.
• Hold-down requirement: supplied with the pad, or existing and reused.
• Orientation: horizontal pad in a vertical vessel, vertical pad, or a drawer arrangement. See demister installation types.

For an existing vessel, measure the diameter at more than one position. A shell may be out of round or locally obstructed, and an unrecognised wall gap can become a bypass path.

Material: specify it now, prove it later

These are two separate stages and should not be conflated.

Specifying happens in the RFQ and is frozen in the quotation or PI as the manufacturing basis. For metal wire and hardware, name the alloy grade. For monofilament products in PP, PTFE or ETFE, name the polymer type together with the raw material producer, its commercial designation and the applicable temperature limits — the polymer type on its own is a family, not a specification.

Proving happens at shipment through the traceability record named in that same PI. Do not leave the specification open and assume traceability or enhanced certification can be added afterwards: by then the material may have been purchased without the required document route, and the necessary records or inspection participation may be unavailable. Meshium does not promise retrospective certification.

Document scope: what is in the price and what is not

Ask suppliers to list the document package explicitly, because this is where apparently identical quotations diverge.

Records normally included in the quoted supply price and listed in the quotation or PI:

• The ordinary material or batch traceability record specified in the PI
• A dimensional inspection record taken against PI-agreed measurement points and acceptance limits
• Product and packing photographs before shipment
• A packing list

Optional items that must be requested before material procurement and production, and that are quoted separately:

• EN 10204 Type 3.1 or Type 3.2 inspection documentation, subject to traceability and mill availability
• Positive material identification and additional testing
• Customer-specified certificate formats and document templates
• Third-party inspection by an accredited agency — decide whether you will appoint and pay the inspector directly or ask the seller to arrange it, and define scope, witness points, location, timing, fees, report recipients and reinspection responsibility before booking

A third-party report evidences only what that inspector actually examined. It does not replace the seller’s own quality obligations, and an ordinary pre-shipment inspection report is not equivalent to EN 10204 Type 3.2.

Commercial fields that change the price

Include these fields so offers can be compared on the same basis:

• Incoterms® 2020 rule and the named place. “CIF” without a port, or “DAP” without an address, is incomplete. Total landed cost, not sea freight alone, is what you are comparing.
• Destination and any inland leg. Port and inland-route choice can materially change total landed cost.
• Packing requirements. Long, non-stackable or easily deformed items need reinforced cases, internal fixing and handling marks. Say if the receiving site has lifting or access limits.
• Delivery window, and whether it is tied to a turnaround date. A fixed outage window is a different commercial risk from a stock replenishment.
• Cargo insurance. For high-value custom items that cannot be resold, insurance scope deserves a line of its own rather than being folded into a freight allowance.
• Payment terms and currency, including which side bears bank charges.

What not to put in an enquiry

This protects you, not only the supplier.

Do not circulate drawings carrying a confidentiality legend to multiple bidders without checking whether you are permitted to. Do not include end-user names, project names, licensor identity or plant location when they are not needed to price the item — they usually are not. Where a supplier needs a category to judge feasibility, a truthful non-identifying description is enough at the enquiry stage; precise declaration details belong to the stage where a supplier has been selected and confidentiality is in place.

If a drawing is genuinely required for quoting, redact what is not needed for manufacture and keep a record of what you released to whom.

What a competent supplier will ask back

Expect these questions. Their absence is itself information about the offer:

• Segmentation constraints and the actual manway path
• Grid material, hold-down method and whether wall sealing is required
• Wash spray presence, coverage and cycle
• Whether an efficiency figure must be tied to a droplet-size basis
• Whether upset cases must be survived or merely tolerated
• Which documents are contractual and which are informational

Why there are no online prices

A non-standard demister’s cost is set by material, density, thickness, segmentation, grids, hold-downs, document scope and packing. A published unit price would have to assume these inputs and may not represent the requested scope. Compare quotations only after confirming that the physical parameters, documents and commercial basis match.

For complete enquiries received on business days (UTC+8), Meshium targets a preliminary sizing or material response within 24 hours. Formal quotation timing is confirmed after requirements, supplier evidence and costing are reviewed and is commonly 2–5 business days for a defined custom scope; complex or performance-guaranteed work can take longer. These are service targets, not contractual lead times. For staged T/T, the applicable PI defines the QA evidence required before the balance request; paid samples and other payment paths follow their own PI, platform or documentary terms.

If it is easier to work from a form, the demister RFQ checklist collects the fields above in one page, and the inspection checklist covers evidence gathering when the item is a replacement.