As featured in Waterline Summer 2021
Implementing a Sustainable Solution for Cooling Tower Treatment in the Food Industry
Mike Hunter – AP Tech Group, Inc.
Abstract
Industrial facilities are continuously looking for ways to improve employee safety and to reduce environmental impact from their operations. Facilities that have multiple cooling systems distributed around a large site are often faced with managing many 20- and 200-litre containers which can have undesirable safety and environmental implications.
It is well known that solid form technologies reduce freight, CO2 emissions, operator handling and exposure and disposal volume to landfill over traditional liquid chemicals. The main challenge is to deliver a full water treatment program cost effectively to take advantage of these benefits across multiple chemicals and at the same time maintain or improve the program performance.
This paper describes how a total water treatment program can be administered using solid chemistries to maximise the safety and environmental gains associated with this form.
Introduction
The company involved is a large food, predominantly milk and milk products producer in the southern hemisphere, with a production rate of approximately 2 to 3 million litres of milk per day. The site also produces powdered milk.
The site chosen for this project has multiple cooling installations around a large area, in a geographically remote part of New Zealand. This denies the opportunity for bulk supply of water treatment products, with the consequence that all chemical deliveries are being supplied in 20kg (44lb) plastic drums, which are subsequently added to containment vessels, local to each system, or in some cases dosed directly from the drum.
Additionally, another major challenge with this site is that it is water constrained, with insufficient means to manage the site effluent. Water reduction initiatives are the immediate focus until capital expenditure is available for water reuse projects in the medium term.
The customer has sustainability targets to meet, including:
1) The total elimination of solid waste to landfills by 2025
2) 100% recyclable, reusable, and compostable packaging only by 2025
3) A requirement for 30% reduction in emissions by 2025
4) A reduction in water usage of 30% by 2025
Along with sustainability goals, the site management team have a high commitment to the health and safety of their employees, and to that of visitors to their facility, and believe that the biggest area of concern is the manual handling hazard giving a high potential for sprains, strains and other injuries, particularly in the case of older employees at the facility. There are additional major issues with the risks of chemical handling and program control:
1) Splashes and spills, causing potentially serious injuries
2) Wastage of products
3) Land contamination
4) Ineffective and potentially untreated systems, caused by the drums running out and not being seen and replaced, resulting in some systems being without treatment for periods of time. This potentially results in scale and corrosion issues, with damage to the assets involved consequently leading to increased costs
5) An increased risk of microbiological fouling, in terms of biofilm formation on heat transfer surfaces potentially leading to microbially induced corrosion, and loss of heat transfer efficiency, therefore increasing operating costs
6) Increased potential for pathogenic organisms to proliferate in the systems in biofilms and potentially being disseminated into the surrounding areas
7) Currently all empty drums are triple rinsed, and sent to landfill whichis a great environmental concern for the customer
The management of the handling and use of the original program was agreed with a traditional approach using 20 kg drums and decanting into local storage tanks or adding chemistry direct from the supplier’s drums as supplied.
The results had also shown some issues with blocking of chemical injection manifolds, with common feeds for all products in use, which has resulted in poor operational results with scaling on the condenser tubes due to this history of poor water treatment.
The above information provided the site management team with an opportunity to look for an alternative approach which would minimise the problems previously described and provide a solution that was safer, more easily operated and with significantly reduced environmental concerns.
Trial overview
A trial using a safer and more environmentally acceptable approach was agreed with the customer involving the use of a solid chemical supply giving reduced handling concerns, a better health and safety profile and the opportunity to minimise the issues previously outlined.
The result was a trial on two cooling systems. System 1 included a Baltimore Air Coil (BAC) counterflow cooling tower associated with a small process heat exchanger (SS 304 Plate and Frame).
Figure 1 – Baltimore Air Coil Cooling Tower
System 2 included a BAC Evaporative Condenser associated with a 600kW NH3 refrigeration plant.
Figure 2 – Baltimore Air Coil Cooling Tower
The opportunity was taken to make some changes to the approach by adding a solid chlorine donor as the primary biocide, but to make this viable it was decided to introduce partial acid dosing using sulfamic acid through a dissolving system locally installed to reduce the pH, and use this control to benefit the operation going forward.
Trial program
A full solids program was introduced to meet the following operational requirement and to assist in the safer operation of the treatment program, along with helping the customer to meet the targets above. The program consisted of a scale and corrosion inhibitor, a stabilized chlorine oxidizing biocide, and an organic acid.
The trial program objectives were to:
• Reduce the risks from manual handling by providing lighter packaging
• Reduce freight and hence CO2 reduction
• Provide entirely recyclable packaging
• Improve control using a dilute chemical solution
• Provide a solids chemical solution pH as near to neutral to eliminate/reduce the risks of blockages in lines and injection quills and manifolds.
Trial equipment & controls
From an equipment perspective, the installation consisted of the use of 4-dissolver arrangement in an enclosure, summarized below:
• Feeder 1 providing addition of a corrosion/scale inhibitor
• Feeders 2 and 3 were combined, to operate as one feed system, for the addition of a solid chlorine donor.
• Feeder 4 was used for providing pH reduction and control by the addition solid organic acid via the dissolver.
• The dissolvers included six Grundfos DDE6-10 dosage pumps which were mounted in a flooded-suction orientation.
Figure 3 – Dissolver Enclosure w/ Dosing Pumps
To control the programs during the trial, a fully automated controls package was utilized, which included the following sensors:
• Conductivity
• pH
• ORP
• PTSA
Control for each of the measured parameters incorporated a 4-20 mA outputs, to modulated blowdown valves and dosage pumps.
Figure 4 – Controls Package
Results
The comparative trial period lasted 6 months, with the existing program evaluated for 3 months followed by the sustainable program. As you can see in the charts below, there were several impacts the trial had on program costs and towards achieving the sustainability objectives:
Figure 5 – Program Cost Comparison
First, and not part of the initial objectives of the trial, the new program resulted in approximately an 18% reduction in overall chemical costs.
Figure 6 – Program Make-Up Water Comparison
Another major impact observed during the trial was the reduction in chemical volume shipped per equivalent volume of make-up water.
As anticipated, the impact on chemical handling including product refills was substantial:
Figure 7 – Chemical Handling Comparison
In the case of refills, the reduction of interactions with the chemical feed system was approximately 36%.
As it pertains to the sustainability goals of the customer, Figure 8 captures the key impacts:
Figure 8 – Environmental Footprint Comparison
Carbon emissions were calculated to be reduced by 94%. Hydrocarbon consumption and plastic to the landfill were calculated to be reduced by 95% each.
And lastly, it was stated by the customer and their refrigeration engineers that they observed at least a 5% improvement in condenser head pressure, improving energy efficiency.
Figure 9 – Condenser Inspection, Fall 2020
Conclusions
The most significant change to the program was to add an acid to reduce pH, to benefit the use of an oxidizing biocide and to allow for an increase in cycles of concentration and reduce the demand for water as this is a water constrained site. The use of sulfamic acid was made because of the supply being solid, having the same means of delivery as the inhibitor and biocide via the dissolvers, along with recyclable packaging as with the other chemicals.
In addition, the monitoring and control of the system was enhanced by the use of a PTSA traced inhibitor to ensure that the levels of corrosion were minimised and water savings could be made by operating at the maximum cycles of concentration.
Through proper due diligence, understanding the customers goals and objectives and conducting a thorough comparative study, sustainable solutions can be identified and implemented for cooling tower applications in the food industry.
