Steam control valves in food and beverage applications

• By Jason Carpenter
• System Integration

Summary

Best practices, such as choosing options with a wide flow range and tight temperature control, ensure reliable service

By Jason Carpenter

Food and beverage applications must meet a variety of process temperature and pressure control requirements to maintain the tight temperatures that ensure product quality and safety. Selecting the right steam control system, and using best practices for piping and installation, can have a huge effect on production, downtime, and the health and safety of end users.

Steam control systems, which include control valves, steam traps, and condensate recovery equipment, are critical in many food and beverage applications. Key applications include clean-in-place (CIP) processes and high-temperature/short-time (HTST) pasteurization used in dairy, cheese, milk, and ice cream manufacturing. Other widely used steam processes include retort sterilization in canning operations, bottle washers, tempered hot water systems, condensate of whey (COW) water, poultry scalders, flash steam peelers and blanchers, evaporators, direct steam injection processes, and hot air dryer systems.

These applications all use a temperature controller with a valve to maintain a separate temperature. The valve is critical, because operators must maintain very tight temperature control to avoid issues that would otherwise occur, like bacteria growth or loss of product.

The challenge faced by many food and beverage applications is that they often do not have a set flow range. This variation of flow ranges is especially true for plants that run different products at different times. For example, at many plants the HTST pasteurization flow can range from 10,000 pounds per hour to 2,000 pounds per hour. To maintain proper temperature control in the face of changes in flow, operators must use a control valve with varying rangeability and excellent shutoff characteristics.

Unfortunately, operators too often use a cookie-cutter approach for steam isolation on modulating process steam equipment. For example, many systems incorporate a pneumatically activated, quarter-turn ball valve to assist in shutting off the steam to the heat exchanger. Users typically select the ball valve because the standard globe valve applications in the market have leaked. Using an actuated ball valve for isolation on the steam train to the process can lead to water hammer, pressure spikes, loss of product, or bacteria growth.

In contrast, a rotary valve has exceptional shutoff and can meet FCI ANSI Class V shutoff on steam for these process applications. This eliminates the need for actuated ball valves for isolation on the steam train to the process. Rotary valves also can enable precise control over a wide range of flows and provide a long service life.

An example is the K-Max rotary globe valve. Its rangeability is 100:1, allowing control over a wide range of flows, so a plant can use the same control valve for all the facility's steam and fluid-control applications. There can be quite an advantage to using one valve style for many applications, because a plant can standardize and minimize stocking requirements.

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Figure 1. This schematic reflects the process heating installation best practices described in the article.

Source: KEI Steam Solutions, Inc.

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Best practices for clean in place

An example of a best-practice installation for a CIP process that performs at high level (figure 1) was developed by Kevin Rasmussen, president of KEI Steam Solutions, Inc. The Green Bay, Wis., industrial machinery and equipment company provides end-to-end solutions to the food and beverage processing industry.

"The setups used today typically require a lot more service and maintenance because they are not laid out or selected correctly and lack best-practice piping, which can cause equipment to fail," said Rasmussen.

Use of best practices increases productivity, reduces downtime, and increases equipment reliability on the systems. "In addition to using best-practice implementation methods, plant operators should always conduct an annual evaluation of steam and condensate equipment to make sure the equipment is running at optimal levels," Rasmussen added.

CIP systems for the food and beverage industry use steam to heat water in the process through the noncontact heating of a heat exchanger, or through direct injection of the steam into the CIP tanks. The rotary globe control valve can be used for heat exchanger temperature control. The turndown allows for maximum temperature and pressure control across a wide range of flow variations. This is critical in CIP heating, where load variations are constant and the application requires consistent temperature control. The application requires very tight shutoff when the system is not in operation, so there is no steam and condensate losses and degradation of the heat exchanger.

Another issue in food and beverage applications is the steam trap and condensate return system, which should remove condensate quickly to allow heat transfer to occur and eliminate the stall point. The best-practice solution includes condensate elimination for the CIP heat exchanger.

Using a Nicholson NFT free-float steam trap allows facilities to continuously remove condensate from the heat transfer surface, allowing for proper heat transfer to the product. Unlike standard float and thermostatic traps, this free-floating steam trap does not have any mechanical linkage. It has a variable orifice that will modulate with the continuous condensate load for fast, efficient condensate removal and process temperature control.

In addition, the best-practices setup also eliminates condensate from stalling or stacking into heat transfer surfaces by using a steam motor or a steam pump and trap combination. When using a modulating control valve, all condensate lines must be drained by gravity or pumped back to the boiler room.

For example, facilities can use a Nicholson condensate steam/air motive pump to recover and pump the condensate back. This eliminates the need for electric pumps, control panels, and wash-down-rated controllers. The ASME-rated pump operates on motive steam or plant air to push the condensate back to the boiler room for energy and utility recovery. Figure 2 shows the standard setup on the top, and the pump and trap combination below. The ideal setup includes a main pressure-reducing valve for reducing the steam pressure to the CIP system from main plant pressure. Examples include a Spence ED or Leslie GPKP.

It should be noted that a best-practice implementation also positions plants to take advantage of energy savings from recovering condensate, which can be like liquid gold to a process. This type of setup helps a plant meet the required balance between energy recovery and food product performance. It also helps answer the question, "How can I maintain my control without having to install costly extra bells and whistles?"

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Figure 2. Condensate recovery using the standard pump option is shown in the top schematic. A pump-and-trap option is shown below.
 

Source: KEI Steam Solutions, Inc.

 

 

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Improper practices

To illustrate the benefits of a steam control system designed in accordance with best practices, consider the example of a large cheese manufacturing facility that recently overhauled its setup from an automated ball valve to the rotary valve setup. Figure 3 shows the "before" state, with a variety of improper practices. These include:

• No drip steam trap was installed for condensate removal before the control valve to prevent valve seat wire drawing.
• The installation has an automated ball valve for isolation directly before the control valve, which offers only on/off service. This will likely cause premature failure of the control valve and heat exchanger tube bundle. It will also cause instability in the process control.
• The control valve is piped too close to the heat exchanger inlet, which does not allow for the velocities to expand out on the pressure reduction through the control valve. The minimum should be 10 pipe diameters of straight pipe run after the control valve of the heat exchanger inlet connection size.
• The heat exchanger should use a continuous-type steam trap or variable orifice steam trap, which continuously discharges condensate to remove condensate from the heat transfer surface and allow for full latent energy utilization.
• The condensate must be gravity-drained to a condensate pump for full condensate removal. This can be done with a steam/air motive pump or electric condensate pump.
• The setup has no thermostatic air vent for the removal of air on startup of the heat exchanger. Without proper air removal, the heat exchanger may experience lagging startup times, improper heat transfer, and air binding of the equipment.
• There is no Y strainer protection before the control valve to allow draining of the piping and removal of scale and debris.

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Figure 3. A Midwestern cheese manufacturing plant “before,” using an automated ball valve and a range of improper practices.

Source: KEI Steam Solutions, Inc.

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Best practices in action

Figure 4 shows the same cheese factory once a new solution was installed following best practices. The seven best practices shown include:

1. A rotary control valve provides tight process temperature control and isolation in one valve. There is no need for a ball valve isolation, because the rotary globe valve allows for 100:1 turndown for process control rangeability, Class V shutoff, and larger CV.
2. Proper piping layout before and after the control valve to the heat exchanger ensures performance will be optimal.
3. The new setup features the correct use of a thermostatic air vent with vacuum breaker on the heat exchanger.
4. Correct discharge piping utilizing a variable orifice free-float steam trap provides continuous condensate evacuation on the heat transfer surfaces.
5. Proper drip pockets and Y strainer protect the control valve from wire drawing of the valve seat.
6. Gravity draining the steam traps to the steam/air motive condensate pump or electric condensate pump provides proper condensate removal from the heat exchanger.
7. Expanding the piping after the steam trap, the setup includes one pipe diameter for a flash allowance from the trap discharge.

Implementation of best-practice equipment selection, piping, and procedures will result in reliable long-lasting service and control of equipment and processes. Because many food and beverage plant operators do not have the technical expertise to ensure the equipment setup is properly implemented, they may be relying on vendors and process equipment providers for this service. That is why promoting best practices is critical to making the process work correctly.

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Figure 4. The cheese manufacturing plant after implementing a rotary control valve and other best practices.

Source: KEI Steam Solutions, Inc.

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