Steam as a living organism
Why a steam system should not be thought of as individual functional items but as an interdependent ecosystem.
Steam systems and boilers are an interconnected system of entities that forms a healthy steam and condensate loop. In carrying energy from boiler fuels, each element relies on the other to perform specific tasks to effectively transfer energy liberated from the boiler fuel to the process application.
To assess the application requirements of the steam and condensate system (The Loop) it is important to consider these interconnections and resulting effects. All components in The Loop must be designed and selected properly with the end point of use steam quantity, quality and purity requirements in mind. If not, the components in The Loop could operate correctly but not achieve the required outcome.
The design and selection process should start at the very beginning of The Loop and look at the:
• Quality of the water being supplied to the boiler
• Boiler water treatment chemicals used
• The boilers’ steam generation rate
• Sizing of pipe work, valves and steam traps
• Requirement for positive condensate removal systems
• Condensate pumps
• Quantity and quality of the condensate returned to the boiler feed system
Many applications in a steam system require steam to be used in direct contact with the end product requiring steam of a very high quality and purity to prevent contamination. Some of these applications include hospital sterilization processes. Steam and condensate system design for hospital sterilization processes must consider the high purity condensate requirement. Condensate water quality that is traditionally generated and returned to The Loop does not meet that requirement.
Standard Condensate purity can be limited due to the following reasons:
• Traditional use of a base exchange softener to remove calcium and magnesium salts to prevent scaling in the boiler
• A chemical water treatment plan to prevent corrosion in the boiler
• Carry-over of boiler water into the steam system resulting in higher than acceptable alkalinity, chloride and sulfate levels
• The steam passing through the steam distribution system, picking up contaminants and carrying them to the sterilizer including Pyrogen levels higher than acceptable parameters.
Pyrogens, the resilient remains of dead bacteria, can remain viable after sterilization. They can only be removed in the boiler feed water pre-treatment section of The Loop by either distillation or ultrafiltration typically utilizing a reverse-osmosis plant. To remove these impurities steam must be produced from a source that can be supplied with reverse osmosis water and does not require the use of water treatment chemicals
Clean Steam Generator
A clean steam generator is a stainless steel vessel that is specifically designed to heat high purity feed water to produce steam using plant steam as the motive or fuel source. The stainless steel construction resists the corrosive effects of the reverse osmosis water allowing Pyrogen free water to be used for steam generation and removes the need for a water treatment program to prevent scale formation.
The steam distribution system will also require stainless steel pipe work and valving to prevent contamination of the clean steam as it travels through the distribution pipe work. Regardless of the type of steam system and components used in steam generation the steam and condensate system is a connected loop. The operation of any one component in the loop will affect the conditions experienced within another part of the loop and often in ways that may not seem related.
When attempting to diagnose problems or make changes in the steam and condensate system the potential effect on the entire steam and condensate loop should always be considered.
- Content provided by Spirax Sarco, originally published in Steam News Magazine.
- Edited by Jessica DuBois-Maahs, Associate Content Manager, CFE Media, Plant Engineering, Control Engineering