Convective tubes

Based on the total combustion volume which includes space between the bed and the convective tubes. 

The inside of the convection tubes rarely foul, but occasionally the Hquid unsaturates in feedstocks tend to polymerize and stick to the walls and thus reduce the heat transfer. This soft coke is normally removed by mechanical means. In limited cases, the coke can also be burnt off with air and steam. Normally, the outside surface of the convection section fouls due to dust and particles in the flue gas. Periodically (6 to 36 months), the outside surface is cleaned by steam lancing. With Hquid fuel firing, the surface may require more frequent cleaning. 

Convection tube spacing is important when the fuel is residual oil or coal, especially co with low asn-fusion or high ash-fouling tendencies. The amount of the ash and, even more important, the characteristics of the ash must be specified for design. 

Vei tical cylindrical cross-tube convection heaters are similar to the preceding type except for a horizontal convective tube bank above the combustion chamber. The design is economical with a high efficiency and is usually selec ted for higher-duty applications 11 to 210 GJ/h (10 to 200 10 Btu/h). 

Honzontal-tube cabin heaters position the tubes of the radiant-section-coil horizontally along the walls and the slanting roof for the length of the cabin-shaped enclosure. The convection tube bank is placed horizontally above the combustion chamber. It may be fired From the floor, the side walls, or the end walls. As in the case of its vertical cylindrical counterpart, its economical design and high efficiency make it the most popular horizontal-tube heater. Duties are 11 to 105 GJ/h (10 to 100 10 Btu). 

In the horizontal-tube box heater with side-mounted convection tube bank, the radiant-section tubes run horizontally along the walls and the flat roof of the box-shaped heater, but the convection section is placed in a box of its own beside the radiant sec tion. Firing is horizontal from the end walls. The design of this heater results in a relatively expensive unit justified mainly by its abihty to burn low-grade high-ash fuel oil. Duties are 53 to 210 GJ/h (50 to 200 10 Btu/h). 

CONVECTION TUBES OD TUBE WALL " ASTM SPEC. ... 

Vibrations in fired equipment and afterburn. Balanced-draft or induced-draft furnaces and boilers are intended to be operated with a small negative pressure (ca. -0.1 in H20), just below the first row of convective tubes, i.e., just below the shock tubes. If we operate such a piece of equipment with a severe shortage of air in the firebox and massive air... 

Select the number of shield tubes between the radiant and convection zones so that the mass velocity of the flue gas will be about 0.3-0.4 lb/(sec)(sqft free cross section). Usually this will be also the number of convection tubes per row... 

CONVECTION TUBES INCHES O.D TUBEWALL INCHE6 MATERIAL ... 

In plants such as oil refineries that have many streams at high temperatures or high pressures, their energy can be utilized to generate steam and/or to recover power. The two cases of Example 1.4 are of steam generation in a kettle reboiler with heat from a fractionator sidestream and of steam superheating in the convection tubes of a furnace that provides heat to fractionators. 

A laboratory scale (nominally 50 kW) combustion system was used to conduct the combustion tests. The over stoker combustor is mounted in a rig comprising a convective tube bank, fouling probe, stack, cyclone and associated sampling, and monitoring equipment. Detailed descriptions of the experimental apparatus are provided elsewhere (9). It should be noted that no secondary air was used in the combustion process. 

Above bed over-fire air is strategically mixed with the volatiles, which consist primarily of CO, COj, CH4, HjO, Nj and tars. Combustion of the volatiles proceeds, the tars are burned out, and heat is transferred to the boiler walls and convective tubes. Reactions above the bed occur first in a reducing environment, and then excess air is added gradually to the upper combustion zone. 

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