Dairy processing industry is evolving

Finding ways to improve energy efficiency.

12/02/2015


Large volumes of hot water are used for manual cleanup and automated clean-in-place systems. Direct-fired water heaters are an opportunity for energy saving here. Photo courtesy of the Wisconsin Milk Marketing BoardAn important element of the food processing universe in the U.S. and Canada is the dairy sector. This includes all of the processes that start with raw milk and produce fluid milk, condensed and evaporated milk, dry milk, cream, butter, cheese and processed cheese, yogurt, whey, ice cream and other frozen dairy desserts.

Consolidation of Processors Continues

According to a recent U.S. DOE ENERGY STAR® Guide for dairy processors, the number of processing facilities continues to slowly decline, while the total industry production volume is increasing. There are still more than 1,500 dairy processing plants in the U.S., and over 440 in Canada. They are located across both countries, with the largest concentrations near dairy farm concentrations.

Dean Sommer is with the University of Wisconsin's Center for Dairy research in Madison. He notes, "There has been tremendous consolidation in the industry, both in terms of closing a lot of smaller and older plants, and in terms of dairy companies buying other dairy companies. On the other hand, similar to the microbrew industry, there has been a trend in recent years for small, artisan cheese plants to spring up. So the big plants keep getting bigger and getting merged into a few huge companies, while a lot of small artisan cheese plants are starting up and creating their own niche in the cheese industry."

Most Energy-Intensive Segment

Dairy processing represents the single most energy intensive sector of the food processing universe. Refrigeration is extensively used not just to maintain the condition of milk, but in cheese aging, yogurt production, and for conversion of liquid milk to ice cream and frozen desserts. Certain dairy products, notably cheese and yoghurt, also require cooking for a significant period of time. This heat energy is commonly provided by steam.

Major energy inputs are also needed for evaporating and drying milk, and especially for drying whey concentrates and solids. Finally, hot water—usually provided by steam—is extensively used for plant sanitation and system cleaning. It is an especially important input for clean-in-place (CIP) systems for storage and cooking vessels and pipelines.

Dairy processing plants, such as this cheese operation, use large volumes of natural gas and electricity in processing raw milk into fluid and dry milk, cheese, butter, ice cream and yogurt. Image courtesy of the Wisconsin Milk Marketing Board

Both Fuel and Electric Energy

According to the 2008 ENERGY STAR Guide, that year the dairy processing industry spent more than $1.5 billion for energy. About half of that was for electricity and half for fuel, largely natural gas. By making the right energy decisions, processes can be streamlined and product quality can be better assured.

Certain areas of energy use are especially worth improving. One such area is the efficiency of steam and hot water production. Boiler upgrade or replacement is important, particularly if plant boilers are aging, and are not optimized for current steam requirements. Where the primary use of the boiler is for hot water production, owners should consider an alternative technology—direct contact water heating.

Advantage of Direct Contact Water Heating

Direct contact systems have efficiencies approaching 100% and, if properly sized, can meet the volume requirements for plant sanitation and CIP systems. In selecting a direct contact water heater, it is necessary to assure that the unit is certified by NSF International for food service applications. If a direct-contact water heating unit meets the operator's needs, the payback from replacing an inefficient boiler can be very short, in some cases a matter of months.

It is important to assure boilers are operating at peak efficiency. Older boilers should be inspected by qualified technicians. Older burner controls can be replaced with digital controls that won't drift or hunt like many older systems, thus improving efficiency. Worth consideration is the addition of an oxygen-sensing capability in the exhaust stream. This will allow the burner to operate more closely to the ideal oxygen ratio.

Refrigeration is another major energy use, as in this refrigerated cheese aging facility. Operators should consider combined heat and power (CHP) systems to meet both electrical load and the need for process heat in the plant. Photo courtesy of the Wisconsin Milk Marketing Board

Improving the Steam System

Downstream of the boiler, if the plant does not have a program for regular inspection of steam traps, one should be instituted. Dairy plants in particular use a large volume of steam, which can mean large volumes of condensate at the traps. If the traps are not functioning correctly or the condensate return piping is inadequate, condensate energy can be lost. Another article in this issue discusses this opportunity in more detail.

Some dairy processing plants still use oil as a primary fuel for boilers. This is clearly a situation that deserves review. Natural gas as a boiler fuel is not only lower in cost, but will result in lower emissions and eliminates the need for exhaust gas treatment. In some cases, operators will want to have a dual-fuel boiler with a supply of fuel oil as a backup in the case of gas delivery restrictions or fuel curtailments.

Another opportunity for major energy savings in dairy processing plants is the use of a combined heat and power (CHP) system for onsite power. A CHP system can carry most or all of the plant electrical load. A gas turbine or an engine-generator can produce large volumes of byproduct heat for process purposes, or as the primary source of hot water for plant sanitation use. According to the DOE Guide, in 2009, only 1% of this industry's consumed electricity was generated at on-site facilities.

Taking Advantage of CHP

According to Sommer from the Center for Dairy Research, CHP could be a valuable addition. However, he concurs with the DOE data, "I have seen very little of this. What we have seen is many plants installing diesel-powered generation systems for emergency purposes. On the other hand, cheese plants basically process fluids and are constantly heating or cooling fluids like milk, whey and various types of water streams." He feels CHP should be included in plant efficiency planning.

It is useful to get expert guidance on sizing and arranging such a system for optimum efficiency. In many cases, the system is sized for the peak plant electrical requirement and additional boiler fuel is purchased as needed. An alternative approach is to size the system for the thermal load and plan to sell surplus electricity back to the local utility. Careful planning and system design can pay major energy dividends.

In many dairy processing facilities, a tri-generation plant might be even more attractive. In this application, the byproduct heat from electric generation is used for both process heating and process cooling, via absorption chillers. As facilities consolidate and get larger, this option becomes even more attractive.

Spray-Drying Milk and Whey

One more dairy area that is highly energy intensive is spray-drying of milk products and whey. Sommers notes, "Most large dairy processors are large users of natural gas, both for boilers but even more importantly for spray dryers for drying of milk and whey powders. Energy costs are a significant part of the processing costs for these technologies. The falling of natural gas prices has provided price relief to many of these companies, significantly reducing their costs of drying these different products derived from milk."

According to the DOE Guide, it is most energy efficient to partially dehydrate the product to be dried first by an evaporative or membrane process. The degree of concentration prior to injection in a spray dryer is dependent on specific characteristics of the product, but experimentation to determine the optimum level is worthwhile. The DOE Guide indicates that complete steam or direct-fired drying can be up to six times as energy intensive without pre-concentration. Also, the optimum drying temperature should be determined. Often increasing the operation temperature actually reduces the overall usage for fuel or steam.

Dairy processing plants are a major opportunity for reduction of energy use, both on the electric side and on the fuel side. Because this is a very specialized industry, attention should be given to university and government research, and to recommendations of dairy processing energy experts.

This articles originally appeared in the Gas Technology Winter 2015 issue.



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