Direct contact heater

Heaters and Heat Exchangers Heat Requirement Heater Duty Specified Heater Heater for a Vapor Fraction Cooler/Condenser Direct Contact Heater/Cooler... 

Deaerator (Direct-Contact Heater) Open heat exchanger in which steam is mixed with water to bring the water to its boiling point. 

Direct contact heater The intermediate liquid at state 2 enters a regenerator where the low-pressure vapor from the turbine (state 7) supplies heat. Heated liquid at the intermediate pressure (state 8) enters a direct contact heater. A direct contact heater is basically a mixing chamber, where the extracted fluid from the turbine (state 6) mixes with the liquid and the hot mixture (state 3) enters into the second pump. The mixture leaves the heater as a saturated liquid at the intermediate pressure. From mass and energy balances of direct contact heater, the fraction of the working fluid extracted from the turbine may be calculated as follows ... 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

Fire tubes, especially in heater treaters, where they can be immersed in crude oil, can become a source of ignition if the tube develops a leak, allowing crude oil to come in direct contact with the flame. Fire tubes can also be a source of ignition if the burner controls fail and the tube overheats or if the pilot is out and the burner turns on when there is a combustible mixture in the tubes. 

Fig. 11. Pebble heater for heating steam to temperatures impractical in metallic units. Also used for heating air. hydrogen, methane, and other gases for processing purposes. In reverse, a pebble healer may be used to recover heat from hot gases. The pebbles are heated in top chamber. 4 by direct contact with combustion gases and passed through a throat to lower chamber B. where heat is transferred to cool gases. The two chambers are maintained at the same temperature so that there will be no gas flow between them. An average cycle on the pebbles is 30-50 minutes...

Immersion Heaters. These devices are lowered directly into a solution for heating. Because the heaters come into direct contact with their solutions, the major... 

Example 4.17 Ideal reheat regenerative cycle A steam power plant is using an ideal reheat regenerative Rankine cycle (see Figure 4.23). Steam enters the high-pressure turbine at 9000 kPa and 773.15 K and leaves at 850 kPa. The condenser operates at 10 kPa. Part of the steam is extracted from the turbine at 850 kPa to heat the water in an open heater, where the steam and liquid water from the condenser mix and direct contact heat transfer takes place. The rest of the steam is reheated to 723.15 K, and expanded in the low-pressure turbine section to the condenser pressure. The water is a saturated liquid after passing through the water heater and is at the heater pressure. The work output of the turbine is 75 MW. Determine the work loss at each unit. 

Heaters can be located in the space between the trms and the dryer housing, where they are not in direct contact with the product, and thermal efficiencies up to 3500 kj/kg (1500 Btu/lb) of water evaporated can be obtained by reheating the air within the dryer. Steam is the usual heating medium. The hi cost of heating electrically generally restricts its use to relatively small equipment. For materials which have a tendency to foul internal heating surfaces, an external heating system is employed. 

Because the boiling model described above is fully explicit, it is rapid and easy to apply. It has been used with success in modelling steam drums and boiler recirculation loops, direct-contact feedwater heaters, high-pressure feedwater heaters, deaerator towers and vessels, condensers and refrigeration loops. The application of the boiling model to a steam drum and recirculation loop will be discussed in the next section because of its importance for the modelling of power stations. 

The Du Pont Model 943 TMA module is shown in Figure 11.4. The apparatus uses a LVDT to sense linear displacements of the sample probe. A thermocouple in direct contact with or in close proximity of the sample is used to detect the sample temperature. The sample and probe are surrounded by a temperature-controlled cylindrical heater and Dewar assembly. Various probe configurations allow the apparatus to be used in the expansion, compression, penetration, tension, stress relaxation, parallel plate rheometry, and fiber tension. The temperature range of the instrument is — 180-800°C an optional furnace can be used to extend the range to 1200 C. 

There are two types of air heaters which can be used in a spray-drying system, e.g., direct air heaters and indirect heaters. Direct air heaters, such as direct gas or oil fired furnace, can be used whenever the contact between combustion gas and spray is acceptable. When products of combustion of fossil fuels cannot contact with the spray, an indirect heater, such as indirect steam air heater, indirect gas, or oil-fired heater, is recommended. Interested readers can find more details about it in the literature (Matsers 1991). 

---