Hybrid pH control strategies to reduce sucrose losses and control corrosion in sugar factory evaporators
Australian sugar factories are amongst the least energy efficient in the world. To maintain the Australian industry’s competitive position and drive the transition to a net zero economy, sugar factories will be required to make substantial changes in energy management and thus operate at significantly higher levels of steam efficiency. For factories seeking to achieve high levels of steam efficiency, extensive vapour bleeding from the evaporator station is usually undertaken. This change in operation typically leads to the juice being exposed to higher temperatures and over longer time. These conditions increase the levels of sucrose degradation that occurs as well as contributing to the formation of acidic condensates that cause premature failure of piping, valves and fittings through corrosion. Sucrose losses and increased maintenance costs due to corrosion impact on the profitability of sugar production.
The control and optimisation of juice pH across evaporation was a strategy identified in SRA project 2017- 007 to mitigate this issue. The aim of this project is to progress the research and commercial implementation of chemical control systems and improved pH control to increase operational efficiencies and mitigate the degradation reactions and associated issues that occur in the evaporators of steam efficient factories.
Objectives
• Determine the safety requirements and suitability for dosing alkaline agents and develop a suitable, reliable and safe design for implementing evaporator station pH control.
• Determine baseline corrosion rates associated with low pH condensate.
• Determine the chemical usage required for achieving the evaporator pH control setpoints with specific alkaline agents and evaluate the impact on condensate pH profiles across the evaporator and ensuing benefits of reduced corrosion.
• Determine the reduction in sucrose losses that can be achieved through evaporator pH control.
• Evaluate the cost and benefits of using a multi-stage factory pH control strategy compared to clarification pH control.
Expected Outputs
The project aims to demonstrate the feasibility of the new pH control system implemented across the clarification and evaporator stations compared to the conventional arrangement where pH control is only applied to the clarification station. Benefits in reduced sucrose losses were demonstrated adopting this new system in the laboratory in the previous SRA Project 2017-007 but required testing at larger scale which will be undertaken in this project to accelerate wide-spread adoption.
The main outputs from the project are:
Feasibility: demonstration of the new chemical processing methodology to provide a simple strategy to be implemented to minimise sucrose losses and maintain condensate pH and reduce corrosion issues when sugar factories adopt extensive vapour bleeding.
– Knowledge: Preliminary knowledge of the reduction in sucrose loss; increase in condensate pH (reduced corrosion propensity); recommended chemicals, dosing rate and dosing locations within the evaporator set; processing costs; any environmental implications and the financial benefit/cost ratio that can be achieved by adopting the evaporator pH control system.
Following this proof-of-concept project, further testing will be required to optimise the system to de-risk for the uptake and adoption by the industry. This will include undertaking longer dosing time trials which will require adopting automatic online versus the manual pH control system that will be used in the project.
The outputs from this project will be available to the milling industry prior to the 2025 season. It is feasible that other mills could implement a similar evaporator pH control system as early as the 2025 season.
No third parties will be required to assist mills in implementing evaporator pH control systems
Expected Outcomes
A common necessity for Australian sugar factories seeking to improve energy efficiency involves the installation of additional heating surface area at the front end of the evaporator set to facilitate extensive vapour bleeding and this also usually requires hotter temperatures to be employed. This has been reported to cause greater than 1% sucrose loss compared to negligible losses in low steam efficient evaporators and this loss has a significant economic impact. SRA project 2017-007 reported that a 0.2% reduction in sucrose loss across evaporation is expected to provide benefits of ~$300,000 p.a. through additional sucrose yield. This was based on the price of raw sugar of $450/t and factory crushing 1.5 Mt cane per year. Additionally, a 10% reduction in maintenance costs to correct corrosion issues was estimated to provide benefits >$50,000 p.a.
Outputs from SRA2017-007 detailed simulations for the Condong sugar factory evaporator station that typically experience sucrose losses across evaporation of >1% and showed that adopting pH control through the early vessels of the evaporator station was able to reduce sucrose losses by >60% and was also expected to lead to reduced lime consumption. However, the cost of new chemicals needs to be accounted. Thus, the project will better estimate the overall benefits and costs for implementing the multi-station pH control strategy.
If successful, a follow-on project involving more extensive and longer testing will be required to better assess the benefits and costs of the multi-station pH control strategy.
SRA PROJECT CONTACT: Muyiwa Olayemi
RESEARCH AGENCY: Sunshine Sugar
CHIEF INVESTIGATOR: Aaron Baker
PROJECT NUMBER: 2024/201
END DATE: 1/07/2025
