Heaters tubular

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."... 

The most common type of commercial pyrolysis equipment is the direct fired tubular heater in which the reacting material flows through several tubes connected in series. The tubes receive thermal energy by being immersed in an oil or gas furnace. The pyrolysis products are cooled rapidly after leaving the furnace and enter the separation train. Constraints on materials of construction limit the maximum temperature of the tubes to 1500 °F. Thus the effluent from the tubes should be restricted to temperatures of 1475 °F or less. You may presume that all reactor tubes and return bends are exposed to a thermal flux of 10,000 BTU/... 

The crude oil and atmospheric residue are heated in tubular heaters. Oil is pumped through the inside of the tubes contained in a refractory combustion chamber fired with oil or fuel gas in such manner that heat is transferred through the tube wall in part by convection from hot combustion gases and in part by radiation from the incandescent refractory surfaces. 

A 1500-W tubular heater is wrapped around the reactor. The autoclave is placed inside a copper pipe, with Fiberfrax bulk fiber insulation packed between the copper pipe and the reactor. Four 1000-W quarter-circle ceramic heaters are placed around the copper pipe. The space between the copper pipe and the ceramic heaters is filled with aluminum balls for efficient and uniform heat transfer from the heaters to the copper pipe. The bottom of the copper vessel is closed with a copper plate. Beneath the copper plate, there are two heaters (a small one of 500 W and a larger one of 1000 W), which are tightly clamped to the bottom copper plate. The top of the copper pipe is similarly covered with another copper plate, and two slots are provided for the feed and product gas lines, coolant inlet and outlet lines, thermocouple extension wires, and the lead wires of the tubular heater. Two ring heaters (660 and 1000 W) are placed on the top copper plate. One thermocouple and a tape heater are placed on the shaft extension to minimize the heat loss through the shaft. No insulation is placed around the ceramic heaters to achieve better control of... 

Delayed coking is a well developed commercial process (6), and operates on a semi-continuous basis. Feed, usually vacuum residue, mixed with steam, is continuously pumped through tubular heaters in which it is heated to its incipient coking temperature. At this temperature the feed is injected into an insulated drum where coking takes place. The vapors produced in the drum during coking are continuously removed and fractionated. The fractions usually include coker naphtha and light and heavy coker gas oils. As a drum fills up, feed is switched to another drum. Meanwhile, the full drum is steam stripped, cooled and the coke drilled out. Whereas feed is continuously supplied to the drum, the coke is recovered intermittently. 

Apparatus for continuous distillation with tubular heater (Burstin and Winkler)... 

To prepare NaaAs, Na vapor is passed over heated As. An iron boat filled with Na is placed inside an evacuated Vycor tube, together with another boat made of sintered corundum and filled with As powder. Using small movable electric tubular heaters, the Na is vaporized at 350-450°C and the vapor is passed over the As, preheated to 180-200°C. Conversion to brown-violet Na3As is complete. The excess Na is removed from the apparatus on heating to 450°C in high vacuum. 

Sanding and polishing oxidized tubular heaters can improve their efficiency 10 to 15 percent. 

Tubular heating elements are extremely durable, resistant to contamination, and quite economical. They can be used on dies, radiant, thermoforming, and hot runner manifold applications. Tubular heaters provide temperatures up to 649°C and offer tremendous design flexibility. 

The major industrial applications of hexagonal boron nitride rely on its high thermal conductivity, excellent dielectric properties, self-lubrication, chemical inertness, nontoxicity, and ease of machining. These are, for instance, mold wash for releasing molds, high-temperature lubricants, insulating filler material in composite materials, as an additive in silicone oils and synthetic resins, as filler for tubular heaters, and in neutron absorbers. On the other hand, the industrial applications of cubic boron nitride rely on its high hardness and are mainly as abrasives. 

Air flows through a steam-heated tubular heater. What would be the effect on heat transferred divided by AT for the following cases (assuming that the air heat transfer coefficient controls) (a) double gas pressure with fixed mass flow rate (b) double mass flow rate (c) double number of heater tubes (d) halve tube diameter. 

Figure 4.56 Nozzle heating by wound tubular heater...

Heat pipes. In an attempt to balance ont the temperatnres along the flow path, the company Dynisco HotRunners has fitted its manifolds with rectilinear tubular heaters, and also with heat pipes (see Figure 4.86). 

Tubular heaters (see Figure 5.10) have found a use in HR system designs because of their potential to bend and be adapted to the shape of the manifold, and because of their good durability and linear temperature characteristic. 

In contrast to other heaters, there is a single coil inside the tube, and the positive and negative wires are located on opposite sides of the heater. This design largely eliminates the possibility of insulation breakdown. The cold ends of the heater, some 50 mm in length, are not heated and should be situated outside the manifold. One operational fault that occurs is that these ends get broken when care is not exercised in servicing. The thermal density of a tubular heater is about 15 W/cm. ... 

When tubular heaters are correctly positioned, a balanced temperature is achieved over the whole length of the flow channel and in the vicinity of the nozzle. Another advantage is the small number of connection leads and the limited munber of heating zones. 

Figure 5.11 Methods of fastening tubular heaters in a manifold...

Heater bending usually takes place on bars fastened to the manifold plate tangentially to the groove curvature, and the heater is pushed into the groove with each bending. The minimum bend radius of a tubular heater depends on its diameter and is 5-16 mm [1]. This technique requires a certain amount of experience. 

Figure 5.14 Principle of arrangement of tubular heaters in manifold block and division into heating zones. Tj and T2 are manifold temperatures.

A mixture of natural gas and circulating gas is taken by compressor 5 and, after the receiver, is mixed with air and nitrogen oxides. Nitrogen oxides are prepared in contact apparatus 6 by the catalytic oxidation of ammonia on a platinum catalyst. The ratio of fresh natural gas to air is 1 2. The methane content in the gas mixture is about 30—33%. The air-gas mixture passes through tubular heater 7 heated by flue gases from furnace 2 and enters reactor 8. 

FIGURE 11.7 Flowsheet of formaldehyde production by the gas-phase oxidation of methane in the presence of nitrogen oxides (process of ICP RAS) [174]. (1) Air blower, (2) furnace, (3) receiver, (4) separator, (5,5 ) compressors, (6) contact apparatus for ammonia oxidation, (7) tubular heater, (8) reactor, (9) pipe cooler, (10) absorber, (11, 15) pumps, (12) receptacle for formalin, (13) scrubber, and (14) cooUng coil. 

Second heater (tubular heater), (8) Transport rollers III, (9) Winding unit,... 

Most commercial fryers are continuous types with direct or indirect heating elements, gas-fired tubes, or high-pressure steam tubular heaters. The most adequate fryers have continuous oil circulation between the fryer tank and the heat exchanger for precise control and distribution of the temperature, as well as metering paddles and a submerger for the control of the residence time. In addition, they are designed to continuously filter out fines and facilitate cleaning. 

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