Define the product passage before the evaporation duty

Start with the catalogued system, not a generic plate frame

The catalogue on this site separates a complete plate evaporation system from the plate pack inside it. The complete system includes feed and preheating, plate heat-transfer sections, vapour separation, liquid transfer, condensation and vacuum equipment, controls and cleaning connections. A plate heat exchanger is a different purchase: it can add or remove heat, but it does not by itself provide the evaporation, separation and concentrate-handling functions of the system.

That distinction changes the questions asked of a supplier. For a complete system, the useful description covers the equipment boundary, the number of effects, whether thermal vapour recompression is included, how vapour is condensed, and how concentrate leaves the package. For a plate pack alone, the conversation is about heat-transfer surface, connections, materials and service access.

A plate pack is a construction, not a complete flow description

The Tetra Pak dairy handbook describes a plate-type falling-film evaporator in which product is distributed through pipes and spray nozzles before passing over heated plate surfaces. Vapour leaves through a cyclone separator at the outlet, and the plate geometry is arranged to keep the falling film workable as the liquid volume falls. That is a specific arrangement described for a dairy duty. It is not a universal description of every machine that uses plates.

The practical point is that the external frame does not tell a buyer how liquid is distributed inside, where evaporation occurs, how liquid returns or leaves, or what pressure conditions apply. Those details belong to the process design and the selected equipment. A supplier should be able to explain the intended product route without relying on a photograph of a clamped frame. If the explanation stops at “plate heat exchanger” or “falling film” without identifying the actual configuration, the product passage has not yet been defined.

This is also why a plate evaporator should not be specified from a heat-exchanger datasheet alone. Plate construction, channel arrangement, porting, seals and operating limits interact with the duty. The quotation should state which of those items are fixed by the proposed design and which remain open pending feed information.

State the particle and rheology envelope at the outlet, not only at the inlet

A liquid that is easy to pump before concentration can become a different handling problem at the target solids. Viscosity may rise, suspended material may concentrate, and foam or entrained gas may change how the liquid moves through separation and transfer equipment. The relevant envelope therefore covers the whole intended run: prepared feed, intermediate concentration and final concentrate.

The FAO juice-manufacture chapter is useful here because it treats preparation, extraction, separation, deaeration, filtration and concentration as distinct unit operations. It also notes that pulpy or viscous puree cannot be passed through a plate or tube heat exchanger because of clogging problems, although such units may become appropriate after solids reduction. That is a caution about feed suitability, not a claim that every plate evaporator has the same passage dimensions or that a particular fruit must be excluded.

For an enquiry, describe the largest particles expected, their source, the preparation step that removes or retains them, and how viscosity is expected to change with concentration. Include foaming and any tendency to deposit on heated surfaces.

Separate the heating duty from the evaporation duty

Heat transfer and evaporation are connected, but they are not interchangeable descriptions. In indirect evaporation, the heating medium stays separated from the food liquid by a heat-transfer surface. The heat raises the liquid to its boiling condition; vapour then has to be separated from the concentrate and handled by a condensation and vacuum circuit. Product, heating and vapour are separate circuits that meet inside the package.

This matters when comparing quotations. One offer may include preheating, effect vessels, condensers, vacuum pumps and controls; another may price a plate section and leave the rest to site scope. Both can be legitimate, but they are not the same system scope. Ask for a boundary drawing or an itemised package list, and identify who supplies the feed tank, cooling water, steam supply, condensate route, cleaning station and discharge connection.

The same discipline applies to performance statements. A water-removal figure describes a duty under stated conditions. It does not establish a feed capacity for another liquid, a guaranteed outlet concentration, or a particular steam consumption without the associated configuration and utilities.

Define the fouling and cleaning evidence before the trial

The dairy cleaning chapter describes deposits forming on heated surfaces and notes that plate heat exchangers can show fouling after a production run. It also treats cleaning as a sequence with defined stages, circulation conditions and verification. Those statements should not be copied as a universal schedule for every food liquid, but they show the kind of evidence to request rather than assume.

A useful trial plan records the feed condition, the operating time, the observed pressure or temperature behaviour, the post-run appearance of the product passage, and the access needed to inspect it. The plan should identify which surfaces can be reached without dismantling the whole package, how the equipment drains, and how the cleaning circuit connects to the evaporator. If the supplier says cleaning is “standard CIP”, ask for the circuit boundary, the intended cleaning media, the compatible materials and the acceptance check.

For the product-passage decision, the minimum is a written statement of what will be inspected, how success will be judged, and who owns each action if the result is not acceptable.

A product-passage brief that can be compared

These answers do not replace a process design or a product trial. They make the first technical conversation specific enough to compare. When the liquid route, the operating envelope and the cleaning evidence are on the table, the evaporation duty can be discussed as an equipment scope rather than a headline capacity.

• Name the prepared liquid and the step that produced it, including any filtration, clarification or phase separation.
• State feed flow, inlet concentration, target concentration and the measurement basis for each.
• Describe particles, pulp, fibres, oil traces, foaming and the expected viscosity at the outlet.
• Identify the intended system configuration and whether the quoted scope is a complete system or a plate section.
• List the available heating, cooling, vacuum, condensate and cleaning interfaces, with the responsible party for each.
• Ask for the inspection and cleaning evidence that will be collected during the trial, not only a statement that the equipment is cleanable.