How Positive Displacement Pumps & Flow Meters Contribute to Product Blending

When a company makes a product for human consumption, all ingredients must be measured to a specific value and added at the proper time in order to achieve the ideal product.

Positive displacement (PD) pumps, flow meters, proportional-integral-derivative (PID) controllers and other mechanical inline mixing devices all play a part in automating food and beverage processes. These devices are what makes large batches of any food or beverage product not only possible, but also consistent. For example, a batch of iced tea requires several ingredients. For the sake of easy math, here are smaller numbers to illustrate the point. There are 822 pounds of product for the iced tea. The breakdown is as follows:

• 500 pounds of water
• 250 pounds of sweetener
• 58.5 pounds of tea concentrate
• 13.5 pounds of citric acid

The blending system being used is designed to produce 200 pounds of product per hour. The time it will take to make 822 pounds of tea needs to be known, so divide 822 pounds of ingredients by 200 pounds per hour rate and it will take 4.11 hours to complete the process of making this batch of tea. Understanding how much product is being added per second will help problem-solve if anything happens to the process flow during the blending run. Not knowing the amount of ingredients being added per second could be catastrophic if something unexpected happens or if the machine malfunctions during the blending process. Customers expect the product to taste the same each time, and the recipe must be followed precisely to meet that expectation. Plus, documentation is needed for each product made, and if the amount of ingredients being blended per second is not being tallied, what was added—and what was not—may not be known. To calculate the set point of each ingredient multiplier used in an automated blending system, first determine the set point multiplier for each ingredient’s total recipe value. The process to determine this is as follows: The formula in Equation 1 will give the set point multiplier and determine the ingredients used per hour:

• 121.7 pounds of water [0.2433 x 500 pounds = 121.7 pounds per hour]
• 60.8 pounds of sweetener [0.2433 x 250 pounds = 60.8 pounds per hour]
• 14.2 pounds of tea concentrate [0.2433 x 58.5 pounds = 14.2 pounds per hour]
• 3.3 pounds of citric acid [0.2433 x 13.5 pounds = 3.3 pounds per hour]

The ingredient flow should be broken down further to determine how much is being added per second. These numbers need to be divided by 60 to determine product total per minute. Additionally, that number needs to be divided by another 60 to determine how much product will be used each second. The ingredients being added per second are:

• 0.0338 pounds of water
• 0.0168 pounds of sweetener
• 0.00394 pounds of tea concentrate
• 0.000916 pounds of citric acid

Now that the flow rate per second is known, set up each ingredient’s totalizer and begin to add up every second. Each ingredient’s total recipe addition weight is available after each ingredient’s set point is introduced into the PID flow controller(s). This will totalize each ingredient’s product flow every second while accurately maintaining the overall product flow. This creates a time slice of flow every second and adds each second’s value to the previous second’s value. This method can be replicated. The primary reason for this degree of accuracy is due to the high cost of ingredients over time. Make sure the flow is being totalized so there is no waste of product or money and repeatable results. Having the flow meter used as a feedback for flow is not all that needs to be done. Each bulk tank of ingredient lines up to an isolation valve, which then flows to the PD pump, continuing on to another valve and then the flow meter, before entering the mix tank. Remember, the flow meter is used simultaneously for ingredient totalization and flow control. By inputting the set point to each of the ingredient’s PID flow controllers, the controller’s output will then ramp up and maintain to match the flow rate used as the set point. The pump is coupled to a motor and the motor speed is controlled by a variable frequency drive (VFD), which receives its set point from the PID controller output. This process is called closed loop control. All of these calculations are critical to maintain product integrity and to allow the recipe to be replicated. By using pumps and systems to control the recipe, the following will be produced:

• a hard copy documenting the recipe, ingredients, time, date, operator, etc.
• a batch number, which allows each batch to be traced
• a batch report explaining how things ran during the process

This data and documentation is important for the recipe to be accurate, replicated and traceable. This is critical when dealing with products for human consumption. Overall, it is important to remember the more equipment being used, the more opportunity there is for contamination to the product being created, so plan accordingly. Automation of pumps and systems is a great way to help with creating large batches of any given product and it can speed up the process. Detailed calculations and knowledge of how the process systems are working can help with troubleshooting, while still maintaining the product quality.