Dual firing

In this example fuel A is a gas over which we have no control. Fuel B is a liquid and its flow may be manipulated to control the heater outlet temperature. The scheme includes a bias feedforward scheme so that changes in fuel A are immediately compensated for by adjusting the flow of fuel B. For this to succeed we have to convert the units of measure of fuel A to be consistent with those of fuel B. By including the heating value of fuel B (NHVi,) in Equation (10.5) we get 

Depending on the choice of units the flow of fuel A (Fa) will now be in TFOE (tons of fuel oil equivalent). In the oil industry the barrel is commonly used as a measure of volume and so BFOE might be used. The output of the temperature controller can be thought of as the total duty demand (in fuel B units) from which is subtracted that delivered by fuel A. 

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Oil-, gas- and dual-fired boilers are available with a range of combustion appliances. The smaller units have pressure jet-type burners with a turndown of about 2 1 while larger boilers may have rotary cup, medium pressure air (MPA) or steam-atomizing burners producing a turndown ratio of between 3 1 and 5 1, depending upon size and fuel. The majority has rotary cup-type burners, while steam- or air-atomizing burners are used where it is essential that the burner firing is not interrupted even for the shortest period. 

WH boilers are usually packaged WT types of dual-fire design because a supplementary fuel is also required. The thermal energy is recovered and used to produce medium pressure (600-900 psig) process steam. 

The most common fuels used are gas (natural gas, methane, propane, synthesis gas) and light fuel oils. Contaminants such as ash, alkalis (sodium and potassium) and sulphur result in deposits, which degrade performance and cause corrosion in the hot section of the turbine. Total alkalis and total sulphur in the fuel should both be typically less than 10 ppm. Gas turbines can be equipped with dual firing to allow the machine to be switched between fuels. 

The burners are located between tube rows. A larger number of burners reduces the heat release per burner and allows a smaller flame diameter and a reduced lane spacing. A ratio of one burner for every 2 to 2.5 tubes provides a uniform heat release. Most burners are a dual-fired design, firing both PSA offgas and supplemental makeup gas. Low NOx burners are used to meet environmental requirements. Makeup gas can be used to induce flue gas into the flame, reducing the flame temperature and NOx level. In a well functioning unit NOx levels as low as 0.03 lb/MMBtu are possible. 

Midstream Delays in construction or expansion of Dual firing capability... 

For most hydrogen plants, the burners are a dual-fired design, which will fire both PSA offgas and the supplemental makeup gas. Lo-NOx burners are typically used to meet modem environmental requirements. In some burner designs, the makeup gas is used to induce flue gas into the flame, thereby reducing the flame temperature and the NOx level. With a properly designed burner, NOx levels of as low as 0.025 Ibs/MM Btu LHV of heat release can be expected. 

Pipes, valves, fittings, and almost all other components of small equipment are now available in plastic or ceramics, which do not corrode in salt water and are less expensive than the metals now used. Synthetic detergents are now available for use with seawater, although a final rinse with freshwater may be desired. Saltwater sewage can be treated successfully. Dual water systems using freshwater and seawater are already in use on ships and in many island resort hotels. Many of these also have seawater systems for fire fighting. This trend will grow. 

As for oil and gas, the burner is the principal device required to successfully fire pulverized coal. The two primary types of pulverized-coal burners are circular concentric and vertical jet-nozzle array burners. Circular concentric burners are the most modem and employ swid flow to promote mixing and to improve flame stabiUty. Circular burners can be single or dual register. The latter type was designed and developed for NO reduction. Either one of these burner types can be equipped to fire any combination of the three principal fuels, ie, coal, oil and gas. However, firing pulverized coal with oil in the same burner should be restricted to short emergency periods because of possible coke formation on the pulverized-coal element (71,72). 

The basis for design overpressure described in this section is related to the ASME Boiler and Pressure Vessel Codes and ANSI B31.3, Code for Petroleum Refinery Piping. Compliance with these codes is a requirement, or is recognized as the equivalent of a requirement in many locations. Where more stringent codes apply, the local requirements must be met. Therefore, local codes must be checked to determine their requirements. For example, some countries do not permit the use of block valves underneath pressure relief valves, unless dual valves with interlocks are installed. Also, in some cases, 20% accumulation under fire exposure conditions is not permitted, and accumulation allowed may be lower than the ASME Codes. In the United States, the ASME Code is mandatory, since it is a requirement under the Occupational Safety and Health... 

This is very common nowadays to allow bargaining on fuel price or to arrange an interruptible gas tariff, which is backed up at times of peak demand with a stored oil supply. Most types of oil and gas burner are available in dual-fuel form, normally with gas burner design wrapped around the arrangement for oil firing. This is usually the more difficult fuel to burn, particularly in the case of residual heavy oils. Fuel selection is normally by a switch on the burner control panel after isolation has taken place of the non-fired fuel. To avoid the cost and complexity of the fuel preheating on oil firing, smaller systems use gas oil as the standby fuel. 

PF burners and fluid beds best meet requirements for dual- and triple-fuel firing including solid fuel as one option. PF burners are particularly suitable, as no static grate exists to compromise the design. They also have a combustion geometry which is similar to gas and oil, and therefore the flame can be arranged to allow full development of flame shape and maximum radiant heat transfer surface utilization. 

Fluid beds can be fired with gas and oil across the top of the slumped bed since sufficient freeboard exists with coal firing to prevent particle elutriation. Oil, gas or dual-fuel burners so arranged could also provide the means for bed preheating, especially if the flame is redirected down to the fluidization zone. 

Opioids act in the brain and within the dorsal horn of the spinal cord, where their actions are better understood. The actions of opioids important for analgesia and their side-effects involve pre- and postsynaptic effects (1) reduced transmitter release from nerve terminals so that neurons are less excited by excitatory transmitters, and (2) direct inhibitions of neuronal firing so that the information flow from the neuron is reduced but also inhibitions of inhibitory neurons leading to disinhibition. This dual action of opioids can result in a total block of sensory inputs as they arrive in the spinal cord (Fig. 21.5). Thus any new drug would have to equal this dual action in controlling both transmitter release and neuronal firing. 

In some cases radiation shields are provided to protect against heat effects from fire incidents and operation requirements. The shields usually are of two styles either a dual layer wire mesh screen or a plexy-giass see through barrier. The shields provide a barrier from the effects of radiant heat for specific levels. They are most often used for protection against flare heat and for barriers at fixed firewater monitor devices, most notably at the helidecks of offshore facilities. 

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Self contained dual agent systems, (foam/water and dry chemical), are provided for manual fire fighting efforts against three dimensional pressure leaks and large diameter pool fires. The design affords fast fire knockdown, extinguishment and sealant against re-flash. A skid... 

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