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Gas Technologies

Furnaces

By definition, a furnace is an enclosed structure in which heat is produced by the burning of fuel. Furnaces can be modified to perform a variety of functions, resulting in them being used by a large segment of industrial and commercial customers. Most often they are used to produce heat for central heating or for melting or heat treating metals and other materials.

  • Furnaces for Central Heating

Furnaces used for central heating consist of two basic components: 1) a combustion chamber, and 2) a heat exchanger. The combustion chamber contains the flame that burns the fuel, producing the heat. The hot products of combustion are then passed through a heat exchanger, which transfers the heat to air for distribution through the building.

In hot air systems, the heated air is distributed to different rooms through air ducts, and the flow of heated air is regulated by dampers. The heated air is discharged through registers located near the floor and it gives off heat as it rises and circulates. At the same time, cooler air is drawn into return ducts located near the floor and is fed to the furnace to be heated and circulated. Central heat provided through hot air systems cannot usually be zoned.

  • Furnaces for Manufacturing Processes

In addition to being used for central heating, furnaces are also used for manufacturing processes. Most notably, furnaces are used in the iron and non-ferrous metal production (aluminum, copper, brass), and metal fabrication industries. In the iron and non-ferrous metal production industries, furnaces are used in smelting, melting, and holding and refining processes. In the metal fabrication industries, furnaces are used to heat metals prior to forging, and to heat treat metals.

There are four main types of furnaces used to produce iron and non-ferrous metals. They are: crucible, reverbertory, cupola, and noncrucible. Essentially, however, the different types of furnaces consist of the same components: a space where the heat is generated, a system for handling the materials, and a draft system. Furnaces used to fabricate metals also are available in various configurations, and are typically classified as either batch or continuous feed furnaces.

The metal production industry in PSE&G's service territory is very small.

  • How Furnaces are Fueled

Through the 1940's the most common fuel for furnaces was coal. Since that time, the use of coal has been replaced by oil and natural gas.

When fueled by oil, the oil must either be atomized (broken into tiny droplets) and sometimes pre-heated to burn efficiently. Atomization is achieved by forcing oil under high pressure through small nozzles, or by using a centrifugal device that spins the oil off a rotating disk or cup. A separate blower is usually used to supply the air required for combustion, which is initiated by an electric arc. Fuels for domestic furnaces are similar to diesel oil, while large commercial units typically use a heavier weight oil.

In contrast, gas furnaces require only a stream of gas and air for combustion. Combustion can be initiated by either a pilot flame or an electric spark.

Furnaces that burn oil can be easily converted to burn natural gas through the installation of a conversion burner. It is not necessary to replace the entire furnace.

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Boilers

A technology commonly used by I&C customers is the boiler. A boiler is closed vessel containing a system of tubes that uses thermal energy to heat water or convert water to steam. Boilers perform multiple functions: the hot water or steam they produce can be used for 1) central heating, 2) water heating, and 3 ) process heating. As a result, boilers are used by a large segment of I&C customers. Steam is also widely used because it is non-toxic and can be easily generated using a variety of fossil fuels.

  • Boilers for Central Heating

When hot water or steam is used to distribute heat, a system of insulated pipes and heating elements (e.g., radiators or convectors) is used. Most hot water heating systems have two pipes attached to the boiler, one for the hot water supply and the other for the cold water return. Some hot water systems operate on gravity (the hot water rises as the cold water drops to the basement for reprocessing), while others are operated by a pump.

Steam systems typically have different piping arrangements, internal steam pressure, and operating temperatures than hot water systems. Because the properties of steam allow it to retain higher heat values longer, steam systems are often used to heat more than one building from a centralized area, thereby eliminating the need for furnaces or boilers in each building. Colleges, universities, and hospitals are examples of facilities that use steam systems. As with hot water systems, once the heat is given off, the condensed steam is returned to the boiler for reprocessing.

  • Boilers for Manufacturing Processes

Because boilers can perform multiple functions, they are used by almost every type of industry to generate steam or hot water for process heating or drying. For example, the textile industry uses a boiler to provide heat for the dyeing and drying of yard goods, the printing industry uses a boiler for processes such as drying, melting, and the processing of photochemicals. Additional uses of boilers are provided in table 2.1. later in this module.

There are two types of high-pressure boilers in use today: fire tube boilers and water-tube boilers.

  • Fire Tube Boiler

A fire tube boiler is a cylindrical tank that consists of a chamber with tubes that are immersed in water. Hot combustion gases flow inside the boiler tubes and the heat boils the water that surrounds the tubes. The resulting steam gathers in the space above the water.

Most of the early boilers, including those used to power steam locomotives were fire tube boilers. Today, most small industrial boilers are fire tube boilers.

  • Water Tube Boiler

In water tube boilers, water is heated in tubes that pass through a fire chamber. Heat from the hot combustion gas outside the tube transfer to the water inside the tube. In absorbing heat from the combustion gases, the water is converted into steam. Steam that is generated is carried to a steam drum.

The demand for greater steam pressure led to the development of the water-tube boiler. Most large industrial boilers (over 50 MMBtu/hour) are water tube boilers.

  • How Boilers are Fueled - Many heavy fuel consuming boilers in PSE&G’s service territory are capable of burning both oil and natural gas. In Modules 4, 5, and 6 the impact of duel fuel capabilities on a customers usage of natural gas will be further explored.

As with furnaces, boilers that burn oil can be easily converted to burn natural gas through the installation of a conversion burner. This is a valid option during the early stages of the life cycle of the boiler.

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Other Gas Technologies for Industrial Processes

Furnaces and boilers are not the only gas technologies used by I&C customers. Other technologies used in industrial processes include: direct-fired process heaters, dryers, kilns, and ovens.

  • Direct Fired Process Heaters

By definition, direct fired process heaters provide heat energy directly to an industrial process without the use of steam or a heat exchanger. Almost every type of industry uses some type of direct fired process heater to heat fluids or solids. Examples of industries that use this technology are the food, textile, paper, printing, chemical, and rubber and plastic industries. The food industry uses direct fired process heaters to cook soups, fry, and sterilize; the textile industry uses direct fired process heaters for washing, scouring, and singeing; and the chemical industry uses direct fired heaters to heat liquids. Direct fired process heaters exist in a variety of forms to serve a variety of functions.

  • Dryers

Dryers are used in manufacturing processes by various industries to remove liquid(s) from a wet solid. Examples of industries that use dryers are the paper, cardboard, wood and lumber, textile, ceramic, tobacco, plastic, paint, food, and pharmaceutical industries. In these industries the dryer might be used to remove moisture used for washing, strengthening the product, or to facilitate handling of the product.

Due to the fact that many industries use dryers, they exist in a variety of forms. The paper and textile industries use cylinder dryers with multiple hot rollers to dry continuous sheets of paper or fabric. The food and pharmaceutical industries use freeze dryers to dry food products like coffee in a frozen state under vacuum conditions. The lumber and food industries use tunnel through circulation dryers to dry lumber, and dehydrate fruits and vegetables. In all, more than a dozen conventional types of dryers exist, and many other industries combine features of conventional dryers to meet their specific needs.

One way to classify dryers is by the heat transfer method they use. There are three general heat transfer methods: direct, indirect, or radiant. In direct dryers the product to be dried comes into direct contact with hot combustion gasses in a chamber and the excess moisture is vaporized and carried away. In indirect dryers the product is not in direct contact with the heat, but it is separated by a separating wall. Often the heat used in indirect dryers is steam generated. Finally, in radiant dryers, infrared or dielectric radiation is used to transmit energy to the product for the purpose of heating and vaporizing the moisture.

Dryers are also classified as batch or continuous operations. In a batch operation the product is grouped together and dried at one time, while in a continuous operation the drying process is uninterrupted, i.e., product is fed through the dryer on a conveyor system.

  • Kilns

Kilns are used primarily by the stone and clay industries to melt and heat different substances. Examples of industries that use kilns are the gypsum, vitreous china plumbing fixture, brick and structural clay, and concrete industries. The four different industries use kilns specifically designed for their needs.

The gypsum and cement industries kilns are used in the calcing process. Manufacturers of plumbing fixtures use kilns to heat and set clay products by passing combustion gases down through a kiln to make the plumbing products more resistant to corrosion. In the production of brickwork and other structural materials, kilns are used to create permanent bonds and improve the strength and performance of the product.

  • Ovens

Ovens are used by industry for low temperature cooking, baking, curing, or to vulcanize (a treatment that stabilizes and adds elasticity) rubber or plastic. The food industry uses ovens to bake bread, cookies, crackers, pretzels, while the rubber and plastics industries use the lower temperature heat produced in ovens in the production of tires, footwear, hosiery, and rubber belts (e.g., fan belts).

While a many different types of ovens exist, they can generally be thought of as batch ovens or continuous ovens. In batch ovens, the product is placed in the oven, heated, and then removed, while in continuous ovens a conveyor system is used to move the product through the oven.

In general, ovens are either direct fired, or heated by steam. In a direct fired oven the heat is generated through combustion of the fuel, while in the steam heated oven, the steam needed to heat the oven is generated in a boiler.

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Other Gas Technologies for Heating

Furnaces and boilers are not the only heating technologies employed by customers for space heating or water heating. This section describes two additional

technologies used by customers to perform those functions. The technologies are water heaters and infrared heaters.

  • Water Heaters

There are four different types of water heaters typically used by industrial and commercial customers. They are: automatic storage, circulating tank, instantaneous, and hot water supply boilers.

  • Automatic Storage

In automatic storage water heaters, the burner, storage tank, outer jacket, insulation and controls are in a single unit. The operation of this type of unit is not dependent upon any other water storage equipment. Residential water heaters are typically of this type.

  • Circulating Tank

A second type of water heaters is circulating tank. Circulating tank water heaters can be classified as 1) automatic, in which the thermostat is located in the water heater, or 2) non-automatic, where the thermostat is located in the storage tank. Circulating tank water heaters are available in a wide range of sizes.

  • Instantaneous

Instantaneous water heaters have little water storage capacity, are self contained, and are often similar to a circulating tank heater. They usually include a flow switch as part of the control system. Instantaneous heaters may have a modulating gas valve that varies gas flow as water flow changes.

  • Hot Water Supply Boilers

Hot water supply boilers are capable of providing high temperature hot water and are operated with a pressure vessel system. They are typically used as an alternate to circulating tank or instantaneous water heaters.

  • Infrared Heaters

Infrared heaters are used to generate heat where typical central heating is impractical. Infrared is the transmission of energy by means of infrared waves. When the waves strike an object they stimulate the molecules within the object to move rapidly and generate heat. The sun is an example of an infrared heat source ¾ approximately fifty percent of the energy receive from the sun is infrared.

Unlike typical heating systems that heat the air, infrared heaters heat surfaces. The amount of heat generated is determined by the physical and molecular properties of the material struck by the infrared waves. Concrete, for example, reacts differently to infrared energy than steel.

Automobile garages and airplane hangers are two locations where infrared heaters are typically found. Both types of buildings have large doors that allow large quantities of air to escape, making typical central heating impractical. In contrast, the infrared heaters offer an economical alternative to central heating.

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Gas Technologies for Cooling

Gas cooling technologies are used by industrial and commercial customers for 1) air conditioning, and 2) industrial refrigeration. Examples of industrial refrigeration include: meat packing facilities, medical and chemical research facilities, and frozen food warehouses.

Gas cooling technologies are rapidly becoming an important option for customers, as they offer several advantages over conventional electric systems. Those who switch to natural gas cooling technologies are able to: capitalize on low natural gas rates, be responsive to the environmental calls to switch to cleaner CFC-free technologies, cut energy costs and eliminate electric peak demand charges, improve indoor air quality economically, be responsive to political calls to use a fuel that is abundant and produced domestically.

Currently, there are three basic types of gas cooling systems available today:

  1. absorption
  2. engine driven
  3. desiccant.

Most manufacturers also specially configure cooling systems to meet customers specific needs. Other systems, called hybrid systems, combine the use of natural gas and electricity. Each type of system is described below.

  • Absorption

A gas powered central absorption air conditioning system uses a very different type of refrigerant to provide cooling. Conventional systems use a chemical substance (CFC’s and HCFC’s) as the refrigerant. Absorption systems use water combined with some other liquid like ammonia or lithium bromide. The absorption process is too complex to fully explain here, but it is important to know that the critical element in the operation of this equipment is heat to boil the water or liquid solution. The waste heat produced from this process can be recovered to provide domestic hot water.

  • Engine Driven

A gas engine driven central air conditioning system operates like a conventional electric driven system with one exception: it replaces the electric compressor motor with a gas powered engine. The engine provides variable speed operation capability, higher part-load efficiency and the potential for engine waste heat recovery for domestic hot water.

  • Desiccant

Gas powered desiccant systems control both humidity and temperature. In desiccant systems, moisture is removed from the air as it flows across a desiccant material. The dried air is then cooled to the desired temperature with an air-to-air heat exchanger or with a gas powered chiller. A heat source, i.e., a natural gas-fired heater or boiler, removes moisture from the desiccant, regenerating it for further use. Desiccant systems are well suited for sites that require low humidity levels or those with high dehumidification loads, e.g., supermarkets, health spas, hotels, medical facilities and restaurants. They also permit precise control of humidity essential for some manufacturing processes.

  • Gas-Electric Hybrid

Some customers opt for systems that combine the use of natural gas and electricity. This type of system is justifiable if electric demand and on-peak energy charges are high. In such installations, the natural gas chiller operates during on-peak periods to avoid the high cost of electricity, and the electric chiller operates during off-peak periods to take advantage of the lower cost of electricity.

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Combined Heating & Power (CHP)

Combined heating and power (CHP) units are basically boilers that generate “free” electricity and use the waste heat of the generation process to provide heating, cooling, and dehumidification (and combinations thereof). There are three basic kinds of natural gas-fueled CHP units:

  • Reciprocating engines
  • Turbines
  • Fuel cells (limited application at present)

If you are a commercial or industrial customer, and want to learn more about this exciting new technology and New Jersey’s CHP incentive program, please visit:  http://www.njcleanenergy.com/html/Combined/combined.html

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