Lots of food and beverage applications need high-quality CO2 measurements, and many in the industry still have questions about how to best go about this. In this post I will explain how to measure CO2 correctly and reliably, while giving an overview of some different requirements and environments.
Why do we need good-quality CO2 measurements?
Whatever the end product, process, or need, the goals are similar in almost all applications: a CO2 measurement that accurately reflects the environment and meets the application requirements. As carbon dioxide results from the metabolism of a living organism and is also an important part of photosynthesis, we cannot ignore its importance when considering process safety, or when discussing productivity or product quality. By understanding how CO2 works in selected processes, we can take advantage of the benefits it offers and optimize our efforts to improve results.
Increasing worker safety
Let’s start with the most important topic – safety. Very high concentrations of carbon dioxide are hazardous because CO2 replaces oxygen. Too much CO2 also has a negative impact on human comfort, which is why most countries enforce workplace exposure limits. For example, in the US the general exposure limit for CO2 is 5,000 ppm over an eight-hour work shift.
It is particularly important to measure carbon dioxide safety levels in the beverage industry: fermentation tanks release CO2 from pressure relief valves in case of overpressure; there is also a risk of gas leakage from tanks or pipelines on soft drink bottling lines. Because CO2 is heavier than air, the gas can accumulate in non-ventilated areas and pose a serious health risk for employees. This is why CO2 measurement sensors should be placed as close to floor level as possible.
Another application that involves safety measurement is refrigeration. CO2 is also known as refrigerant R744 and is much more environmentally friendly than many other gases previously used in refrigeration. It is widely used in supermarket and grocery store chill cabinets, cold rooms, walk-in freezers, and industrial cold storages. As with all refrigeration systems, leaks can occur over time due to poor maintenance practices, mechanical wear, accidental damage, improper installation, or simply because CO2 refrigeration systems typically operate at high pressures.
Without properly maintained CO2 monitoring equipment leaks can go undetected as CO2 is an odorless and colorless gas. Although Vaisala CARBOCAP® products are not safety approved, many customers have found they work well for early warning and general monitoring purposes. In order to detect CO2 as quickly as possible, transmitters should be installed close to potential leakage points such as flanges, valves, pressure reducers, or pumps.
High productivity is essential in modern manufacturing. Businesses in the food industry typically produce large volumes with low margins, making productivity and effectiveness essential in order to stay in business. Greenhouses are good examples of how yield can be controlled by CO2. There is a sweet spot of CO2 concentration where cucumbers or lettuces grow best. In this case, CO2 is used as a fertilizer for the plants, meaning that ensuring the correct concentration is critical: too much or too little will affect the quality of the produce.
Optimizing product quality
A more recent application of CO2 is fermentation and enzyme manufacturing, for example in the textile, paper, food, and baking industries. Fermentation usually takes place in a bioreactor, and careful monitoring is essential. CO2 is a by-product of the process and its concentration needs to be monitored to see how the process is developing.
CO2 can also be used to increase and maintain product quality. Adding CO2 to food packaging can considerably extend the storage and shelf life of meat, cheese, fruit, and vegetables. For example, a high CO2 concentration in meat packaging inhibits bacterial growth and maintains the natural color of the meat. In a similar way, a high CO2 concentration slows down or stops the fruit aging process in long-term storage or during transportation.
Sensors often need to be placed inside a duct, chamber, or machine. The measurement spot is sometimes located close to the ceiling, meaning it is high up and difficult to access. In these cases, it’s beneficial to use sensors with long-term measurement stability to minimize the need for additional sensor checks. Depending on the application, it might be better to use a separate sample pump and tubing to transfer a gas sample into a remote CO2 instrument rather than trying to install the sensor directly into the process. For example, it is not possible to place sensors inside a hot oven, but gas samples can be easily drawn from the process. It might also be economically justified to build a sampler, which takes gas samples from several different spots. With the help of a multiplexer, each sample can then be measured sequentially using a single detector. If there is no need for continuous, real-time measurement this arrangement is possible, but if non-stop measurement is required, a dedicated sensor is needed for each location.
Keeping your sensor clean
Good hygiene must be observed in food industry processes. Sensors must therefore withstand common detergents such as alcohol-based cleaning agents or hydrogen peroxide (H2O2). In addition, sensor surfaces must be designed in such a way that they are easy to clean simply by wiping, with no holes or seams. The sensor must not be made out of any material that will release harmful chemicals or have parts that could easily become loose and drop into the process. Environments like dusty poultry houses with many spots to monitor pose additional challenges for measurement. Mushroom farms, where the whole room is cleaned regularly with a pressure washer, require all equipment including CO2 sensors to withstand direct water jets.
Maintaining your CO2 sensor
Even if your sensor equipment has long-term stability and accuracy, in the long term there is always some need for sensor maintenance. Some sensors are disposable and the whole unit is replaced – for example, chemical cell-type sensors are single-use. Depending on the sensor age, there can also be some issues with the detection sensitivity of this type of sensor. Disposable sensors might be a costly choice in the long run as replacement costs start to add up.
A more economical option is to use CO2 sensors that are protected by replaceable filters. Dirty filters that have dirt, oil, or dust buildup prevent gas exchange with the sensor and should be replaced.
Aging CO2 measurement instruments should be calibrated against a known reference or sent to the manufacturer for service. A separate, recently calibrated handheld instrument can be used as a reference meter. Comparison between the handheld meter and the CO2 measurement instrument gives a simple indication if the sensor needs service.
Learn more about measuring CO2 in demanding conditions and join our free webinar on 19 March.
For more information about our smart CO2 products, visit our web site: GMP251 and GMP252, or contact us.