High accuracy, low-flow color dosing with Coriolis mass flow meters

High accuracy, low-flow color dosing with Coriolis mass flow meters

Many liquid laundry detergents are easily recognized by their distinct blue color. The addition of such blue coloring and other fluorescing agents adds trace amounts of dye to fabrics, both counteracting discoloration and improving brightness.

Fun fact: Bluing in history

A popular method of laundry bluing used into the 1900s involved a product called “Reckitt’s Blue-Bags” which contained one-ounce squares of synthetic ultramarine and baking soda. Before this product was created, clothes were whitened with a blue dye made from finely ground cobalt-containing glass.

Challenge: Inaccurate, inefficient pumps lead to noticeable variation

Modern blue dyes and fluorescing agents come in extremely high concentrations, so color dosing systems must add in very low doses during detergent production. The high concentration also means slight variations in dosing can lead to noticeable variations in the appearance of end products.

Dosing and metering pumps are often used to regulate color dosing systems. Under constant temperature and pressure conditions, the displacement of the pump can be used to infer an accurate flow rate. However, fluctuations in temperature and pressure alter fluid properties and therefore decrease the accuracy of flow measurements. Pump wear and tear can also decrease system accuracy and repeatability. While these pumps are often fairly inexpensive themselves, process inefficiency can be costly.

Solution: Coriolis flow meters accurately measure low-flow liquids

It is now common to find flow meters added into color dosing systems as an extra safety net of process monitoring. The flow meter monitors flow downstream of the pump in the color dosing system, providing real-time feedback to the pump over analog signals or a range of industrial protocols. This automated monitoring of the dosing process minimizes costly process inefficiencies and wasted batches, and ensures process repeatability.

Coriolis technology provides repeatable, high-accuracy mass flow readings for liquids and gases at very low flows. In the diagram below, a CODA-Series mass flow meter is located downstream of a pump, enabling fine-tuning of the amount of liquid dosed into the final product.

CODA Coriolis flow meter in line with pump for liquid dosing application

CODA Coriolis mass flow meter in line with pump for liquid dosing application

CODA mass flow meters can be used to measure low-flows with high accuracy and repeatability:

  • Accuracy as good as ±0.2% of reading or ±0.05% of full scale (whichever is greater)
  • Repeatability of ±0.05% of reading or ±0.025% of full scale (whichever is greater)
  • Full-scale flow rates down to 40g/h

Additionally, these instruments are built with inherent insensitivity to external vibrations and disturbances, minimizing process disruptions. They also have no need for annual calibration.

In the video demonstration below, you can see a CODA controller (meter with additional valve) flowing water at ultra-low flow rates:

Discuss your process with an applications engineer