Brazed plate heat exchangers are made by brazing a stainless steel plate pack using a material such as copper to create a strong inter-plate bond — this seals the unit permanently and creates unique operational challenges with regards to cleaning and maintenance. This style of heat exchanger is compact and efficient, leading to wide use in HVAC, hydronic heating, steam heating, as well as industrial applications with a wide variety of process fluids. These units utilize relatively narrow flow channels to promote efficient heat transfer, making them particularly sensitive to adverse effects from fouling and mineral buildup. For system operators and heat exchanger cleaning companies, it is important to consider best cleaning practices and system conditions to ensure brazed plate heat exchangers operate effectively and according to specification. This article provides a brief overview of the methods and benefits of cleaning and maintaining brazed plate heat exchangers, as well as operating considerations to ensure effective long-term service.
The Importance of Maintenance for Brazed Plate Heat Exchangers
As plate heat exchangers undergo regular use, suspended solids and organic materials in process fluids settle on heat transfer surfaces, creating biofilms and other fouling layers. Similarly, dissolved minerals in hard water lead to the development of scale on heat exchanger plates as they precipitate at high temperatures experienced in the unit. These buildups lead to reduced thermal performance as heat must transfer across these layers in addition to the width of the plates themselves — they also reduce the internal channel volume between plates, increasing pressure drop and leading to increased pumping energy and/or reduced fluid flow rate.
These factors prevent the heat exchanger from operating under the design conditions it was intended to, compromising performance and potentially leading to sub-par product output with contamination in production applications and ineffective heating or cooling in HVAC applications. It is critical to perform cleaning and maintenance at recommended service intervals to extend equipment service life, stabilize energy costs and other operating expenses, and ensure operational needs are met.
Standard Methods and Best Practices for Cleaning
The cleaning intervals of your brazed plate heat exchanger depend on a number of factors, including the process media, temperatures, and specific application; consult with the heat exchanger manufacturer and vendor for specific cleaning guidelines. As brazed plate heat exchangers are permanently sealed, the plates cannot be accessed for individual mechanical cleaning/replacement; therefore, chemical cleaning practices are a must for brazed plate heat exchanger maintenance. CIP (Cleaning in Place) via chemical solutions dissolves and flushes fouling and scale deposits and can also provide a passivating effect to maintain corrosion resistance of the plates.
Before beginning, shut off relevant pumps, isolate the heat exchanger, and drain and depressurize both sides of the unit; use proper protective equipment such as safety gloves and eye protection when handling cleaning agents. Pre-flushes with water may be performed in alternating directions to dislodge debris. Prepare CIP fluids to the specifications of the supplier and attach portable CIP systems to the inlet and outlet connection of the heat exchanger.
CIP fluids include caustic solutions with approximate pH ranges of 7.5-10 for removal of organic deposits and phosphoric solutions for removal of inorganic deposits such as limestone. There are many specialized fluids available for CIP — for example, there are agents specifically designed to neutralize the remnants of other CIP fluids before performing a final water flush. The main flush is often performed in reverse or both flow directions at 70%-150% of the normal operating flow rate for 30-120 minutes. The final flush should always be performed with potable water, monitoring the system for standard pressure, flow rates, and temperatures to confirm restored performance; ensure a complete flush is performed before returning the unit to service. Spent CIP solutions must be properly disposed of according to local environmental regulations.
Other Design and Operation Considerations for Extended Service Life
Corrosion leading to ineffective operation and mechanical failure can be inhibited by maintaining optimal water chemistry and avoiding incompatible fluids such as cooling brines with chloride salts. Regular pH and chloride-level testing in conjunction with water treatment/replacement, as well as preventing stagnation of process fluids, aids in preventing corrosive deterioration of your brazed plate heat exchanger. General best practices to prevent degradation and reduce the frequency of cleaning cycles include:
- Using inlet strainers and filters to filter particulates.
- Maintaining stable water chemistry (pH, hardness, oxygen levels) to limit scaling and corrosion.
- Avoiding thermal shock (large temperature swings).
- Monitoring system performance against standard parameters to ensure cleaning is performed with appropriate, fluid timing rather than at preset intervals.
Brazed plate heat exchangers in Canada use colder source water and/or use glycol mixtures to prevent freezing, which necessitates special design considerations. Colder source water is often correlated with a higher level of dissolved minerals that precipitate at operating temperatures, forming scale faster relative to warmer climates. Designing and operating brazed plate exchangers for Canadian markets means considering the viscosity and flow rate impacts of glycol solutions, and implementing maintenance practices for glycol-based units. Glycol must be replaced regularly as part of preventative maintenance, as repeated heating leads to breakdown of additives, and increases the risk of biofouling.
The first step in keeping your brazed plate heat exchanger clean and well-maintained is to selecting the right heat exchanger from the right supplier with the expertise and product base to provide the optimal solution. Partnership with Valutech ensures access to a strong supply chain and a product lineup to suit the needs of virtually any application with recommendations for models that can be maintained long term. This article is a brief introduction to brazed plate heat exchanger maintenance — for more information on available models, their features, and recommended maintenance practices, please contact Valutech here, or see the full brazed plate heat exchanger lineup here.