Continuous Liquid Flow Furnaces

Continuous liquid flow furnaces include boiler furnaces, fluid heaters (such as Dow-therm heaters), evaporators, cookers, and many liquid heaters used in the chemical process industries. (See figs. 1.12 and 4.25.) The tubing through which the liquid fluids flow is often built as an integral part of the furnace, for which many textbooks are readily available therefore, they will not be discussed at length here. 

The boiler and chemical process industries also have learned (1) that the flame and hottest poc should traverse a radiation section first, then flow through a convection 

Circulation by the burner gases helps convection, raises triatomic gas concentration (for more gas radiation to all sides of the tubes), and lowers NOx emissions. With large burners, use of adjustable thermal profile burners can optimize uniform heating to the coils. 

Many small, high-velocity burners might improve heat transfer if installed to fire between the tubes and the refractory walls. 

If the first bank of convection tubes can see the burner flames or hot refractory, its life may be shortened by the overdose of radiation. These are therefore called shock tubes. The shock can be lessened by piping the coldest feed liquid into those tubes first. If hot combustion products are on one side of the heater (heat exchanger), and if the fluid feed on the other side of the heater tubes is a gas or vapor, the danger of tube burnout is greater because gases and vapors generally have poorer thermal conductivity than most liquids. 

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Binary liquid metal systems were used in liquid-metal magnetohydrodynamic generators and liquid-metal fuel cell systems for which boiling heat transfer characteristics were required. Mori et al. (1970) studied a binary liquid metal of mercury and the eutectic alloy of bismuth and lead flowing through a vertical, alloy steel tube of 2.54-cm (1-in) O.D., which was heated by radiation in an electric furnace. In their experiments, both axial and radial temperature distributions were measured, and the liquid temperature continued to increase when boiling occurred. A radial temperature gradient also existed even away from the thin layer next to the... 

There are many different reactor designs but the two most commonly used are fixed bed and batch slurry phase. For a fixed bed reactor a given volume of solid particulate or monolith supported catalyst is fixed in a heated tube located within a furnace and liquid and/or gaseous reactants flow through the bed. This type of process is commonly used for large continuous-volume production where the reactor is dedicated to making only one product such as a bulk chemical or petroleum product. 

Data for liquid phase adsorption are typified by water treating for removal of small but harmful amounts of impurities. Some conditions are stated by Bemardin [Chem. Eng., (18 Oct. 1976)]. Water flow rates are 5-10 gpm/sqft. When suspended solids are present, the accumulation on the top of the bed is backwashed at 15-20 gpm/sqft for 10-20 min/day. The adsorbent usually is not regenerated in place but is removed and treated in a furnace. Accordingly, a continuous operation is desirable, and one is simulated by periodic removal of spent adsorbent from the bottom of the vessel with a design like that of Figure 15.18(b) and replenishing of fresh adsorbent at the top. The pulses of spent and fresh carbon are 2-10% of the total bed. Height to diameter ratio in such units is about 3. 

The apparatus for open-tube diffusion consists of a silica furnace tube with a continuously flowing gas. The exit end may be at atmospheric pressure or at reduced pressure. The impurity source may be a vaporizing solid whose vapors are carried to the semiconductor by a carrier gas. The carrier gas may be bubbled through a liquid impurity source. The carrier gas takes up source molecules, which then decompose at elevated temperatures. Liquid sources are maintained at or near room temperature. This arrangement has an advantage over the use of solid sources in terms of easier control of source temperature and, thus, impurity concentrations in the carrier gas. 

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