Plant efficiency by interrogating mixing performance in reactor tanks

Reactor vessels, whether they be anaerobic digesters (AD) or other water treatment reactor tanks, tend to deviate from ideal mixing conditions over time. This can have a huge impact on plant performance resulting in a range of issues. A lithium tracer test is regarded as one of the most effective techniques to interrogate mixing efficiency so that smooth operations can be maintained.
Mixing efficiency is a common metric to interrogate plant performance against contractual requirements during commissioning and at regular intervals during plant operations.

Factors such as gradual grit deposition in the reactor tanks can reduce mixing efficiency leading to reduced active volume, dead zones and short circuiting which can all have a direct impact on plant performance, safety, failure to comply with permits and lower revenue generation. When left unmonitored, grit accumulation can account for active volume reductions of up to 8-10% per annum, resulting in a rapid drop off in plant performance and energy output.

Operators can choose from methods going – from rudimentary thermal imaging – to dyes – to more comprehensive tracer testing to interrogate the mixing efficiencies and active volume of their reactor vessels. While thermal imaging is a quick test to highlight issues, it struggles to provide a complete and accurate assessment especially in the case of insulated tanks. Tracer testing, on the other hand, while being more resource intensive than the former, provides detailed operational parameters within the reactor vessels. Performed at regular intervals the tracer tests provide valuable insight and can help operators take proactive, informed decisions to maximize revenues, prevent major failure events and keep within permits.

A Lithium tracer test is regarded as one of the most effective technique to interrogate mixing efficiency, buildup of grit and sediment, hydraulic retention time and short-circuiting in reactor tanks either of CSTRs or plug flow configurations. Activated sludge treatment plants are typically plug flow while AD reactors are CSTR.