Alkalimeter
Main benefits:
- A more stable purification process without significant changes in the alkalinity of the pre-lime and main-lime juice.
- Saving of over-used lime milk, dosed above the required amount, above the required pH of the purification juices.
- CO2 savings associated with excessive consumption of lime milk in the purification process.
General description
A fast and reliable analysis of the parameters of the purification juices is essential to ensure efficient control of the purification process. Automated analysis allows periodic and automated monitoring of juice parameters to optimize process control, as opposed to less frequent, time-shifted and time-consuming manual laboratory analysis. The system enables the sugar refinery to better control the purification process, resulting in savings of over-used lime milk and the associated consumption of limestone, coke and reduced CO2 emissions.
The system allows the measurement of pH, alkalinity and total calcium content of the pre-lime and main-lime juice. Compared to the conventional colorimetric laboratory method, where the moment of colour change is determined and a certain amount of acid is calculated to calculate alkalinity, the automatic system does not rely on visual but on instrumental pH measurements. The results of both methods are comparable.
On the basis of the measured values, the lime dosage can be changed more frequently and more accurately to optimise the sugar juice purification process.
A computer system, through which configuration and management is carried out, allows the analysis of pre-lime and main-lime. Samples are pumped to a central measuring point. The system measures pH, alkalinity and total Ca++ content. A certain volume of juice is measured and withdrawn. The temperature of the collected sample is reduced to 20 °C to achieve constant results. A pH measurement is taken at this cooled temperature. The sample is then titrated with sulphuric acid to a target pH of 8,09 and the alkalinity of the sugar juice is determined by calculation. To determine the total lime content, the titration is continued with sulphuric acid to a target pH of 2,5. The instrument then waits until all chemical reactions have taken place and titrates the sample with sodium hydroxide to a target pH of 8,4. The calculation of the titration yields the amount of total lime in the original solution.
Sampling
The pre-lime or main-lime juice is fed into the sample collector. The analysed juices are automatically fed into the reactor of the instrument where the measurements are carried out.
The presence of small inclusions and abrasive components does not affect the operation of the system.
Measurement procedure
The sample is transferred from the collector to the titration reactor. The reactor is a glass vessel with a water-cooled outer jacket through which water flows from the cooling circuit. This casing and the temperature control system reduce the sample temperature to 20 °C. The reactor is filled by direct feed from the collector. The filling is limited by a reactor overflow which limits the sample to the required volume. The reactor is first flushed with water and then the sample is filled. The pH sensor, temperature sensor and level gauge are lowered into the reactor. When the sample temperature is close enough to 20 °C, the pH measurement is started. After a successful measurement, the titration process is started. The endpoint criterion for titration is set according to the parameters specified by the client. Based on the data obtained, the alkalinity of the samples is calculated.
In addition, for lime-saturated juices (pre-lime and main-lime juice), the total lime content is calculated. Two different titration reagents are used, sulphuric acid for titration and sodium hydroxide for back titration to determine the total lime content.
The analysis of the parameters of the individual juices is carried out according to a user-defined periodicity. The alkalinity of the juices can be measured more frequently than Ca++.
Automatic system cleaning cycle
The system is designed so that it does not need to be shut down and manually cleaned during the campaign. Basic cleaning is performed after each sample is analyzed to maintain constant measurement quality. Periodic deeper acid cleaning occurs periodically after a certain number of samples have been analyzed. The user can determine after how many samples a deeper cleaning is performed.
System control
The instrument can be controlled via the touch panel. In automatic mode, the measurement of individual juices rotates according to the requirements of the sugar factory.
The control program parameters for the automatic mode can be set individually for the following process steps:
- automated sampling
- filling of the titration reactor
- titration procedure using automatic burettes
- discharge of the reactor
- cleaning procedures
In manual mode, it is possible to run any measurement or manually control individual components of the instrument, e.g. filling the reactor with a specific juice, filling with water, cleaning and controlling valves or individual pumps.
The instrument’s memory can be consulted for results, warnings and error messages on the instrument display or remotely via the Ethernet port.
System advantages
- More precise control of the purification process based on regular measurements.
- Reduction of lime milk consumption during the purification process and associated reduction of CO2 emissions.
- Automated measurement
- Simple calibration of the instrument
- Automated cleaning
- Manual cleaning of the instrument is only necessary at the end of each campaign
Typical measurement duration per sample:
- approximately 15 minutes for a complete measurement;
- approximately 8 minutes for pH and alkalinity measurements only.
System requirements
Supply voltage: 230 V + 10% – 15%, 50-60 Hz, 2 kW
Water supply: pressure 6 – 10 bar
Air supply: 8 – 10 bar
Operating temperature: 10 – 40 °C
Operating fluids
1 N HCI – 3 l/day
0.1 N HCI – 5 l / day (for cleaning the device)
1 N NaOH – 3 l / day