I. First, determine the equipment type based on the "total evaporation capacity"

The processing capacity is the primary determining factor, directly deciding whether to choose a single-effect, multi-effect, MVR, or batch/continuous system.

1. Small processing capacity (≤ 10 tons per day)

Suitable for: small enterprises, laboratories, batch wastewater, food samples, and traditional Chinese medicine concentration.

Selection points:

Use batch low-temperature vacuum evaporators or small kettle-type, wiped-film evaporators.

An evaporation area of 1–10 m² is generally sufficient.

No multi-stage system is required; a water ring pump for vacuum is sufficient.

Quick start-stop, small footprint, and low investment.

Suitable for: 1–3 tons per day, or 3–10 tons per day but not continuous.

2. Small to medium processing capacity (10–50 tons per day)

Suitable for: most chemical plants, food factories, electroplating wastewater, printing and dyeing wastewater of medium scale.

Selection points:

Choose continuous falling film evaporators or forced circulation low-temperature evaporators.

A single-effect system is basically sufficient; if steam is cheap, a single-effect can be used, and if steam is expensive, a double-effect can be used.

The heat exchange area is generally 10–50 m².

A Roots + water ring vacuum system is sufficient, with stable operation and simple maintenance.

Continuous operation, high efficiency, and moderate energy consumption.

This is the most mainstream range in industry.

3. Medium to large processing capacity (50–200 tons per day)

Suitable for: chemical wastewater, high-salt wastewater, electroplating parks, large food factories.

Selection points:

Use multi-effect low-temperature evaporation (2–4 effects) or MVR evaporators.

The heat exchange area is usually 50–200 m², and multiple units in parallel are also common.

Multi-effect systems save significantly more steam than single-effect ones; MVR has lower operating costs than multi-effect systems.

It is crucial to be equipped with a stable vacuum system, automatic control system, preheating section, and CIP cleaning.

Suitable for continuous and stable working conditions.

4. Large processing capacity (≥ 200 tons per day)

Suitable for: power plant desulfurization wastewater, chemical parks, seawater desalination, high-salt solid waste leachate, etc.

Selection points:

Priority is given to MVR low-temperature evaporation or multi-effect + MVR combined systems.

The heat exchange area can reach several hundred square meters or even thousands of square meters.

Adopt multi-stage series connection, continuous feeding, and continuous crystallization.

The equipment investment is the highest, but the long-term cost is the lowest.

High reliability is required, with full automatic control and remote monitoring.

II. Determine the evaporator specifications based on "flow rate per unit time"

In addition to the total daily volume, the processing capacity also depends on the peak flow rate; otherwise, choosing a too large one will be a waste, and choosing a too small one will lead to overload.

1. Determine the effective evaporation capacity

Effective evaporation capacity = feed rate × (feed concentration − discharge concentration) ÷ discharge concentration.

Only after clarifying this value can you correspond to the evaporator area.

2. Basic relationship between area and processing capacity (general experience)

Single-effect falling film low-temperature evaporator:

Generally, 1 m² of heat exchange area ≈ 20–40 kg/h evaporation capacity (depending on the material).

Forced circulation:

1 m² ≈ 15–30 kg/h.

MVR:

High energy efficiency, 1 m² can correspond to 30–60 kg/h, or even higher.

In engineering, coefficient correction is performed based on material boiling point elevation, viscosity, scaling tendency, and vacuum degree.

III. Determine the area coefficient according to material properties to finalize the model

The processing capacity is only the "target", while the material determines "how much area is needed".

1. Low-viscosity, clean water-like wastewater

→ Large area coefficient, more compact equipment selection.

For example: 1 m² ≈ 30–40 kg/h.

2. High-viscosity, high-salt, easy-to-scale materials

→ Small area coefficient.

For example: 1 m² ≈ 10–20 kg/h.

Forced circulation or wiped-film evaporators must be used; otherwise, the heat transfer efficiency will be insufficient.

3. Heat-sensitive materials

→ Must be selected in the high-vacuum and low-temperature range, but the area requirement remains unchanged.

4. Easy-to-foam, easy-to-emulsify materials

→ Area requirement increases because the evaporation intensity needs to be reduced to avoid material entrainment.

IV. Final selection formula (directly used in engineering)

First calculate: total evaporation capacity G (kg/h)

Then estimate: evaporation capacity per 1 m² K (kg/h·m²)

Calculate the required area A = G ÷ K

Finally, match the market standard models:

Common models are 5 m², 10 m², 20 m², 30 m², 50 m², 100 m²...

When selecting, a 10–20% margin must be reserved to cope with future increases in water volume, scaling, and viscosity increase.