Clayton Armstrong 2011-02-22 GSK Aranda SP - steam&condensat

STEAM AND CONDENSATE AUDIT

Project N°30275

Date: 04/02/2011

GSK MANUFACTURING Aranda, Spain

Page 40 of 45

Established by E. Morin

To the attention of Ms. Beatriz Herrero-Gonzalo

11 Appendix N°2: Steam Pressure Controlled Heat Exchangers at Low

Load

11.1 Current situation

Within the steam system, there are several pressure controlled heat exchangers operating at low

loads. Within these heat exchangers, liquids or gasses (air) are heated along with the steam. Most

of the time the desired medium temperature is below 100°C, and the heat exchanger is working at

partial load. Under these conditions, regardless of brand or model, problems may occur due to the

physical properties of the steam.

An audit is only a short visit on site, in which it is impossible to see all operating conditions. Most

problems with heat exchangers only occur at certain conditions. For instance, operation of heat

exchangers for building heating may only be a real problem during the fall and the spring, when

partial loads are typical. Due to the variability of these problems they are often not recognized in

time, and can cause process bottlenecks, loss of production, loss of temperature control and

increased maintenance costs.

Control of steam pressure can be designed in two ways: modulating or on-off. In both cases the

control valves are modulated by the measured temperature of the heated media. Steam pressure

controlled heat exchangers at low loads almost always produce sub-cooled condensate.

Modulating Controls

The steam pressure after a modulating control valve is always lower than the steam pressure in the

up steam lines, unless the system is working at full load which is a rare operating condition.

When heating a product to a temperature below 100ºC, the required steam temperature will often be

close to 100ºC, as the latent heat of the steam is used to transfer the energy as the steam

condenses. Steam temperatures lower than 100ºC, has a pressure below atmospheric pressure. If