Energy Conservation through Proper Condensate Recovery
Siddharth Jain
Product Manager C Steam Systems
Forbes Marshall

Increasing fuel cost have led to increase in steam cost, which is an area of concern for the process industry. Most chemical plants have adopted energy savings measures to optimise their fuel consumption in boilers. Article offers recommendations to reduce energy bills through effective condensate evacuation and maximising Condensate Recovery Factor (CRF).

Steam has been used as a working fluid or utility media throughout industry not only for mechanical power production(ie, driving steam turbines to produce electrical power) but also for many space heating and process applications. The advantage of using steam as the working fluid is due to the ease of distribution and control. Fuel prices across the world are on the rise which has resulted in an increase in steam cost and hence an area of concern for the process industry.

When steam transfers its heat to any process, it is the enthalpy of evaporation, which is transferred first, and the steam thus condenses back into water at the same temperature. Steam utilisation and condensate management, in a proper engineered way, plays a crucial role in bringing down operational costs. This directly impacts the revenue savings for the industry and thus become the need of the hour.

Most chemical plants have adopted energy savings measures to optimise their fuel consumption in boilers. This ensures the best steam cost in day to day operation of their steam boilers. In a typical process plant, the boiler generates steam to meet the steam demand of the process. Any optimisation in the steam utilisation leads to reduction in the steam generated. Thus, optimum steam utilisation for the process direct impacts the annual fuel bill.

The chart below indicates the spiralling cost of solid fuel price used for steam generation in the span of 10 years - 2.8/kg to 6.2/kg(CAGR of 8.27 percent, ahead of inflation in most years)

For optimising the annual fuel bill it is recommended to focus on the following two broad categories:

1. Effective condensate evacuation by selecting the correct type of steam trap along with the essential accessories

2. Maximising Condensate Recovery Factor(CRF), ratio of condensate recovered to the total steam generated

1. Proper Selection of Process Steam Trap - Effective Condensate Evacuation

A fundamental step for ensuring optimum steam consumption for any process application is to ensure selection of right type of steam trap. Proper selection of steam trap must consider many factors; a few of them are listed below:
  • Quick plant start up with continuous venting of air and incondensable gases
  • No tolerance for loss of steam under all operating conditions
  • Efficient temperature control/steam consumption through effective condensatedischarge
  • Self-draining to prevent damage from freezing during plant shutdown
  • No disruption of operation if the trap fails
  • "All-in-one design," with a strainer, check valve and air vent
  • Rugged construction for least maintenance costs
  • Robust internals for delivering high up-time
In the industry, very often the procurement of steam traps is based on the lowest cost and not on the overall cost of ownership. The total cost of the steam trap should include tangible incidental costs, such as piping cost, steam loss through the failed trap or the steam loss due to the bypass valve kept cracked open, reduced production output, loss of production due to frequent downtime. Taking such factors into consideration such as, reduction in the overall cost of installation, operation and maintenance is critical .

2. Benefits of Condensate Recovery
When steam heats the process liquid, around 75 percent of its energy is transferred to process and steam condenses. Balance 25 percent energy is held by the condensed water. The condensate is pure water, having almost zero TDS, which is ideal to be used as boiler feed water. Since it is at a higher temperature, less fuel will be required to produce steam. Every 6 Degree Celsius rise in feed water temperature saves 1 per cent on the fuel bill.

In a nutshell, the advantages of condensate recovery would be

1. Elevated boiler feed water temperatures
2. DM quality water
3. Minimises the amount of chemicals required to treat boiler feed water
4. Minimises water usage that is critical in most geographical locations
5. Effective return can lower load on cooling tower, overall costs thus positively influencing profitability
6. Addresses environmental concerns, norms (Zero Liquid Discharge)

In the chemical industry, one of the major concerns for condensate recovery is the fear of contamination.

Modern day solutions help in recovering the effective heat from contaminated condensate, thus enabling optimised condensate recovery factor.

Case Study:
Proper monitoring and control of process parameters in the following major areas of steam consumption in a chemical plant facilitates energy savings:

1. Multiple Effect Evaporator section(comprising of stripper, MEE and ATFD section)
2. Solvent Recovery Unit ( SRU)
3. Multi Utility Reactors ( MURs)

The optimisation of above processes is mainly achieved with

1. Correct process temperature control - PID based instead of On-Off control valves
2. Optimised steam condensate evacuation systems (evacuation of condensate even under stall conditions)
3. Segregation and recovery of pure steam condensate from Multi Utility Reactors

These solutions have been implemented at a major chemical plant in Vishakhapatnam, and results are close to ideal.

Section-wise challenges and solutions
  • Steam condensate evacuation issues from Agitated Thin Film Dryer (ATFD) due to group-trapping
  • Stripper condensate evacuation issue thereby requiring the bypass valves to be always kept cracked open (due to stalling)
  • Huge wastage of flash steam from this section
  • To save the cost of additional steam traps and related installation and maintenance issues, a single steam trap is used to drain condensate from the multiple sections of the ATFD. This practice is commonly termed as "group trapping".

    On the face of it, this sounds perfect as due to common pressure, chances of water logging are eliminated. In reality, no two coils or heat exchangers are identical. Even though the pressure at which steam is received by both heat exchangers is same, the heating loads will vary differently. As a result, the pressure difference will come in the picture and the section at low pressure will be unable to discharge. Along with this, the pressuredrop taking place across each of the heat exchangers will be different. Pressure drop taking place in a heat exchanger depends of a large number of parameters like: fouling factor, process temperature profile, ambient temperature ,etc. It is quite clear that all these parameters are beyond manual control and if group trapping is done, it will result in issues like water logging and damage to the equipment. Installation of correct size and type of individual process trap for draining condensate from each section of ATFD instead of group trapping.
  • "Stall" is the reduction or the cessation of condensate flow from the steam space, and occurs when the pressure in the steam space is equal to, or less than, the total backpressure acting on the steam trap. Stripper condensate evacuation was optimised by installing a process trap that can evacuate condensate even under negative differential pressure thus optimising removal of condensate.
  • Closed loop condensate management system such that the flash steam from ATFD is recovered in the Stripper and the condensate is then recovered at elevated temperature ( >100o Celsius).
Solvent Recovery Unit (SRU)
  • Solvent Recovery Unit condensate evacuation issue from the columns thereby requiring the bypass valves to be always kept cracked open (due to stalling)
  • Manual operation of steam inlet to the process always led to fluctuations of +/- 5oC in the column bottom and top temperatures also disturbing the reflux and recovery rate
  • Installation of adequately sized PIDbased temperature control valves with proper position indicator indicating the percentage of opening under varying load conditions.
  • Stripper condensate evacuation optimised by installing a process trap that can evacuate condensate even under negative differential pressure thus optimising removal of condensate.
Multi Utility Reactors (MURs)
  • Recovery of pure condensate from MUR due to fear of contamination with cooling water.
  • Recovering of pure condensate from reactors using heat optimisation segregation units and recovery of condensate through steam operated condensate recovery systems at elevated temperatures
The chart below indicates the impact of the above recommendations on the overall condensate recovery factor for the plant.

Addressing the issues mentioned above led to a 18 percent increase in condensate recovery and direct saving of 7 percent in the annual fuel bill .

The benefits of modern day energy conservation methods are now being realised, and slowly but surely replacing traditional methods in the chemical industry. This not only will help the plants attain their energy conservation goals and reduce their carbon footprint, but also contribute to a healthy bottom line that is crucial to stay ahead in a competitive market place.