Gas combustion heaters

Day-to-day running costs. Energy costs for gas combustion heaters are about one-fourth of those for electric heaters. 

Catalytic gas combustion radiant heaters have generated substantial interest. The combustible air-gas mixture is introduced to the heater directly below a porous bed of catalyst that is similar to the catalyst used in automotive exhaust systems or camper heaters. Combustion and radiation occur at the catalyst surface. Catalytic gas systems are desired for their uniform surface temperature and low operating cost. Lack of temperature modulation is the major problem with gas combustion heaters. The catalytic gas system needs many gas lines and controls, as well as, an electric heater that must preheat the catalyst bed prior to initiating combustion. As a result, the initial installation cost is very high compared to the allelectric heating systems. 

Initial installation cost. Large panel heaters require fewer connections than ceramic heaters. Catalytic gas combustion heaters require electrical and natural gas installations and extensive gas control and monitoring. 

Occurrence. Carbon monoxide is a product of incomplete combustion and is not likely to result where a flame bums in an abundant air supply, yet may result when a flame touches a cooler surface than the ignition temperature of the gas. Gas or coal heaters in the home and gas space heaters in industry have been frequent sources of carbon monoxide poisoning when not provided with effective vents. Gas heaters, though properly adjusted when installed, may become hazardous sources of carbon monoxide if maintained improperly. Automobile exhaust gas is perhaps the most familiar source of carbon monoxide exposure. The manufacture and use of synthesis gas, calcium carbide manufacture, distillation of coal or wood, combustion operations, heat treatment of metals, fire fighting, mining, and cigarette smoking represent additional sources of carbon monoxide exposure (105—107). 

Unvented kerosene and gas space heaters leaking chimneys and furnaces back-drafting from furnaces, gas water heaters, woodstoves, and fireplaces automobile exhaust from attached garages environmental tobacco smoke. Humans are normally the main indoor source of carbon dioxide. Unvented or imperfectly vented combustion appliances can also increase indoor COj concentrations. 

Pellistors are used to detect flammable gases like CO, NH3, CH4 or natural gas. Some flammable gases, their upper and lower explosion limits and the corresponding self-ignition temperatures are listed in Tab. 5.1. This kind of gas sensor uses the exothermicity of gas combustion on a catalytic surface. As the combustion process is activated at higher temperatures, a pellistor is equipped with a heater coil which heats up the active catalytic surface to an operative temperature of about 500 °C. Usually a Platinum coil is used as heater, embedded in an inert support structure which itself is covered by the active catalyst (see Fig. 5.33). The most frequently used catalysts are platinum, palladium, iridium and rhodium. 

If intentional chemistry is performed, chemical reactivity hazards can be expected to exist at your facility. An exception is intentional, essentially complete combustion with air, such as the burning of propane in a gas-fired heater. The burning of ordinary flammable and combustible materials has been excluded from our definition of chemical reactivity hazards and is adequately treated elsewhere. If the answer to Question 5 is YES, then the rest of this section on intentional chemistry need not be considered further, and you should proceed to Question 2 at the beginning of this chapter. 

A number of studies have documented that concentrations of some of the directly emitted species found in outdoor atmospheres can be quite high indoors if there are emission sources present such as combustion heaters, gas stoves, or tobacco smoke. In addition, there is evidence for chemistry analogous to that occurring outdoors taking place in indoor air environments, with modifications for different light intensities and wavelength distributions, shorter residence times, and different relative concentrations of reactants. In Chapter 15, we briefly summarize what is known about the chemical composition and chemistry of indoor atmospheres. 

In addition to what appears to be a heterogeneous chemical source for HONO, it has also been shown to be emitted directly from combustion systems. For example, it has been measured in the exhaust of noncatalyst-equipped automobiles (Pitts et al., 1984b), from natural gas combustion in a kitchen stove, and in the emissions from kerosene and propane space heaters (e.g., Pitts et al., 1985, 1989 Brauer et al., 1990 Febo and Perrino, 1991,1995 Spicer et al., 1993 Vecera and Dasgupta, 1994). 

This plant also uses propane driven fork-lift trucks and at the time of the survey direct gas fired heaters were being used to warm the air in the plants. Both of these combustion sources would contribute nitrogen oxides to the air. 

Carbon monoxide Carbon monoxide is an odorless, colorless, and toxic gas. Sources of carbon monoxide volcanic activity, internal combustion engines, unvented kerosene and gas space heaters, generators and other gasoline-powered equipment, tobacco smoke. 

A major fire erupted in a nonflammable solvents manufacturing unit in a U.S. Gulf Coast chemical complex. A furnace tube in a natural-gas-fired heater ruptured due to overheating. At least 1,800 gallons (6,800 liters) of a combustible heat transfer fluid spilled and burned intensely. Within about 25 minutes, the intense hot fire damaged four levels of structure and associated process equipment. The plant on-site emergency squad quickly and properly responded. However, the price tag for short-lived incident was over 1.5 million in direct property damage and over 4 million in business interruption (U.S. 1979). Fortunately, there were no injuries. [2]... 

Plans were under way to return a reactor to service. This gaseous phase reactor requires a startup temperature in excess of 500° F (260° C). A natural gas—fired heater provides the heat energy to a circulating combustible heat transfer fluid and the heat transfer fluid flows through the reactor tubes until startup temperature is reached. 

How much energy is needed for a natural gas water heater, like the one shown in Figure 14.18, to heat the hot water in your home It is probably much more than you think In the next Sample Problem, you will find out. You will also calculate the heat of combustion of a hydrocarbon the heat that is released when combustion occurs. 

Absolute Humidity—the ratio of mass of vapor (moisture) to mass present in the carrier gas stream. Example 0.02 pounds of water per pound of air. This number can be used to find the relative humidity on the psychrometric charts. It is also useful for cumulative quantities in a stream due to such items as products of combustion (when a gas fired heater is used), and evaporation and ambient quantities. This is necessary for calculating condenser or venting amounts. 

In consumer s use, applications of gas sensors related to environmental pollutant gases are carried out mainly for security and amenity. Examples of the applications are, for instance, in the protection from a incomplete burning of combustion apparatus for home use and in the ventilation or condition of indoor atmosphere. A combustion monitoring sensor using SnOj was developed by Tanaka et al.[110] of Figaro Engineering, Japan. The gas water-heater... 

Flameless gas-air heaters also have been designed. They have a cylindrical body made of porous refractory ceramic material. After the ignition of the air-gas mixture, a flameless combustion takes place within the pores of the heater s ceramic body. The flameless burning has two advantages (a) the fuel combustion is very complete, and (b) the bottomhole zone does not become fouled with soot. During the combustion process, the body of the heater becomes red hot, radiating the heat into the oil-bearing bed. In another variant, the porous ceramic piece is placed direcdy on the wellbottom in such a manner that it encloses the perforated body of the heater like a jacket. 

Flue- Large pipe through which fumes escape from a gas water heater, furnace, or fireplace. Normally these flue pipes are double walled, galvanized sheet metal pipe and sometimes referred to as a "B Vent". Fireplace flue pipes are normally triple walled. In addition, nothing combustible shall be within one inch from the flue pipe. 

Thermal regeneration uses heat to combust binders and contaminants. All thermal processes need an initial mechanical step in order to bring the sand to the correct grain size and to screen out any metallic contaminants. This pretreatment may also involve a (partial) abrasion of bentonite and dust removal. The heating of the sand is usually achieved by means of a fluidised bed furnace, operating at temperatures mostly between 700 to 800 °C. Rotary kilns or multiple-hearth furnaces are also used. Heat may be provided by gas combustion, electric heaters or by short wave infra-red emitters. The throughput of these systems ranges from 250 kg/h to more than 5 t/h. 

Direct air heaters are less complicated, and drying air temperatures up to 800°C can be obtained. Gas-fired direct heaters have been used more frequently in recent years because of the increasing availability of natural gas in many parts of the world. The fuel (or gas) combustion rate Mq (kg/s) is given by... 

Heater efficiency can be affected by the excess O2 content or extra air for combustion and a high stack temperature. Inappropriate O2 content could be caused by lack of control, air leaks, and poor burner performance, while a high stack temperature corresponds to high heat loss in flue gas. A heater approach temperature, defined as the temperature difference between flue gas to the stack and heater feed inlet, could be caused by heater fouling in operation and by heater design. 

The more rigorous way compared to O2 measurement is to measure CO in the flue gas. This can be accomplished by measuring combustibles in the flue gas. Combustibles here refer to the products of incomplete combustion including CO, hydrogen, and trace hydrocarbons, while CO accounts for the majority of combustibles. For consistency with O2 measurement, the combustibles measurement should be taken in the same location as the O2 analyzer. With reliable combustibles measurement available for ppm concentration, it allows the 02% level to be reduced safely (safety margin) until the combustibles start to increase (Figure 5.11). This is the optimal 02% for the heater. 

That can be the case with carbon monoxide poisoning. Carbon monoxide is an odorless, tasteless, colorless gas produced by the incomplete combustion of carbon-based fuels such as natural gas, fuel oil, charcoal, or wood. It can be emitted by any improperly installed or poorly maintained combustion source such as unvented kerosene or gas space heaters, furnaces, wood stoves, gas stoves, fireplaces, or water heaters. 

A major fire erupted in a nonflammable solvents manufacturing unit in a US Gulf Coast chemical complex. A furnace tube in a natural-gas-fired heater ruptirred due to overbeating the heat transfer fluid trapped in a stagnant tube. At least 1800 gallons (6800 L) of a combustible heat transfer fluid spilled and burned irrtensely. Within... 

The dryer provides heat to volatilize the solvent and a means to carry the solvent away from the coating. Efficient hardware is used to minimize energy costs. The dryers may be equipped with the appropriate pollution abatement devices to meet both OSHA and EPA standards. Dryers commonly use hot air both to provide heat and to carry away the solvent. The air may be heated by steam or by heat exchange with flue gases. Flue gases from the combustion of natural gas maybe used directly in place of hot air. Infrared radiant energy from gas combustion or electric resistance heaters is sometimes used. Conduction heat transfer from heated... 

Initial installation cost. Plate and panel heaters require less electrical connections than ceramic brick heaters. Catalytic combustion heaters require both gas and electric connections. 

As in gas-fired heaters, the objective of an operating engineer should be to ensure complete combustion of the oil fuel with minimum excess air. A few of the more common troubles peculiar to oil burning that cause excess air to be increased are ... 

The feed air preheats to about 1,300°F in a gas-fired heater. The gasifier is designed to operate at 20 atmospheres pressure and to convert only about 50-70% of the coal to fuel gas. Therefore, recovery of a large amount of char in the hot raw coal gas for direct combustion is necessary. VEW now appears to favor dry sulfur recovery fi-om the coal gas via a circulating fluidized bed of limestone. Alternatively, VEW is considering designs with no coal gas desulfurization, thereby increasing the amount of sulfur dioxide in the flue gas fi om the pulverized boiler. 

Heat balances are determined for all the reactor models discussed. Therefore the heat duties of the radiant tubes, convection section heaters, waste heat boilers, and assoeiated steam drums are all explicitly calculated and reported. Heat losses are part of the models, as described in the Heat Losses section. The enthalpies of all the streams entering and leaving each piece of equipment are caleulated and reported. These streams include, for example, the process, fuel, air, and flue gas. Combustion, and all reaction related heat effects, are handled in models using enthalpies of all species including heats of formation based on of the elements at their standard states, so heats of reaction are avoided. 

Maintenance cost. Heater efficiencies, replacement of reflectors, required cleaning, replacement of broken quartz glass heaters, and incomplete gas combustion are some major issues. Ease of identification of bumed-out heaters is also important. 

---