Multiple and simple effect stills

Puretech offers world leading solutions for purified and highly purified (water for injection) water systems.

Our multiple and simple effect stills take pre-treated water through a series of treatments to produce pyrogen-free Water For Injection that meets all USP standards.


Puretech multiple effect Water for Injection Stills are designed and constructed to produce pyrogen-free sterile water (WFI) in full compliance with cGMP guidelines as per FDA and EMEA requirements. Engineering and manufacturing practices follow ISO 9001 procedures, ASME BPE criteria, GAMP guidelines, etc. Design and construction meets the most stringent Regulations and Codes from Europe, USA and others concerning safety and pressure vessels.

WFI applications

WFI water for injection, as defined in the Ph Eur and the USP, is used for the preparation of medicines for injectable administration, where water is used as a vehicle (water for injections in bulk), to dissolve or dilute substances or preparations for injectable administration before use (sterile water for injections). According to the Ph. Eur water for injections can only be produced by distillation, of drinking water or purified water.

To ensure the equipment meets your requirements, we work in partnership with you and a dedicated team follows your order as a unique project. We develop specific Quality Plans (DQ, IQ and OQ) and undertake factory acceptance testing (FAT) to give assurance, performance and quality.

Operating principle

Feed water (PW) is pre-heated by means of two DTS heat exchangers, which use respectively the heat of the pure steam and distillate water outlet and the plant steam outlet. The first column of the CS water still is equal to our CPS steam generators, heated also with plant steam. The pure steam produced in the first column is used as the heating medium for the next one, so it condenses and turns into WFI. Simultaneously, the partial amount of non-evaporated water goes to the next column, so it is also partially evaporated as pure steam and used as heating energy for the next column. Here, the pure steam also condenses (resulting in WFI distillate) and it is transferred by pressure to the successive columns.

Control system

The control system is based on a PLC wire operator supervision via a user-friendly touch-screen HMI with the following menu:

  • Mimics of the equipment, showing the operational state in real time
  • Process parameters (temperature, pressure and conductivity)
  • Setting up of parameters
  • Alarm information
  • Start-up and alarm recognition.

Options include: paper or electronic chart recorder for pure steam conductivity, temperature, extra feed water conductivity meter, online TOC monitoring, etc

Multiple effect stills

A multiple effect still consists of a series of pressure columns divided into two parts: a double tube sheet (DTS) heat exchanger that acts as an evaporator, and an upper column used to separate pyrogens; preventing drops carrying impurities from reaching the end of the column. The separation column’s diameter has been designed to obtain a sufficiently slow upward speed for the drops carrying impurities, to fall to the bottom of the column under the effect of gravity. The multiple effect still design increases the energy contribution from the mains steam by providing steam circulation successively around the various columns in the still.

Simple effect stills

A simple effect still is basically the same as the first distillation column of a multiple effect still and supplies pure steam to a condensing unit. The energy and steam consumption of a multiple effect still is much lower, since it reuses the steam calories to generate more steam and at the end of the series of columns the steam reaches the condensing unit at a lower temperature. Nevertheless, contrary to general belief, the number of effects does not affect the quality of the end product.

Design and Construction

Compact and modular

Puretech still unit and all components such as feed water pump, pre-heater and condensers are mounted on stainless steel AISI 304 skids. All parts in contact with the media are made of stainless steel AISI 316L, insulated with mineral wool (asbestos-free material) with external cladding made of stainless steel AISI 304. Inner surfaces are polished to Ra < 0.64 μm and electro polishing is an available option. Hygienic design: Including clamp connections, orbital welding techniques for tubing and components, minimisation of dead legs and proper piping slopes for self-drainability, double tube sheet construction in first column, condenser and pre-heaters, diaphragm valves for distillate/reject, etc.

Simple and efficient design

The lower part of the column consists of a double tube sheet shell heat exchanger with a large central pipe surrounded by a bundle of peripheral seamless pipes. This arrangement produces a natural fluid circulation: ascendant inside the peripheral pipes and descendant inside the central one. Steam flows up very slowly but droplets cannot reach the top of the column as they fall down simply by gravity. Thus, impurities such as particles and pyrogens contained in the droplets are dragged down towards the bottom of the column where they are automatically blown down. Pure steam from the first column serves as heating energy in the next column where it condenses as WFI. This can be reproduced several times, so called multiple effects, up to 7 columns. The more effects we install, the less heating energy and cooling water required.

Ease of maintenance and installation

The heat exchangers are totally accessible and no internal elements are located within the column. This makes inspection much easier than other designs, with long pipes or internal heat exchangers. The replacement of column gaskets can be done easily and quick, without needing to dismantle the column, which removes the need for very high technical areas in order to take off any internal part. Heat exchanger pipes are always totally immersed in water, so there is a very low tendency to build up scale inside the tubes. Moreover, as they are shorter than other designs, they are less stressed by vibrations and risk of corrosion is significantly reduced.

Options and accessories

  • Feed water conductivity monitoring
  • Pure steam take from the first column
  • Elevated WFIS condenser
  • Hot standby mode
  • Sanitisation/Sterilization of the separator columns and WFIS condensers
  • Protective mesh guarding
  • On-line TOC monitoring device
  • WFI storage and distribution skid



Puretech engineered and installed a purified water to system at the AstraZeneca Research and Development Centre, Cambridge , taking raw water from the mains through purification using OASYS units. The purified water, which is stored in a 5000-litre tank, is distributed via a stainless-steel ring main to user points in the laboratories.

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