Steam rate/heat duty

Short regeneration tune requires a higher steaming rate, thus increasing the heat duty of the condenser system. 

The statement that the mass, or weight flow of vapor through the trays, increases as the refluxed rate is raised is based on the reboiler being on automatic temperature control. If the reboiler were on manual control, then the flow of steam and the reboiler heat duty would remain constant as the reflux rate was increased, and the weight flow of vapor up the tower would remain constant as the top reflux rate was increased. But the liquid level in the reflux drum would begin to drop. The reflux drum level recorder controller (LRC) would close off to catch to falling level, and the overhead product rate would drop, in proportion to the increase in reflux rate. We can now draw some conclusions from the foregoing discussion ... 

What would happen to a steam reboiler if the float in the steam trap became stuck in a partly closed position, or if the steam trap were too small Water—that is, steam condensate—would start to back up into the channel head of the reboiler, as shown in Fig. 8.3. The bottom tubes of the reboiler bundle would become covered with water. The number of tubes exposed to the condensing steam would decrease. This would reduce the rate of steam condensation, and also the reboiler heat duty. 

Now the rate or heat duty of steam condensation is termed Q ... 

The steam specification stipulates the need for superheated steam at 380°C and 4000 kPa. This medium-pressure product is of sufficient quality for the plant steam-turbine and ammonia superheater, with the remaining portion to be sold to another plant. A heat balance over the entire steam-production circuit concludes that this steam product may be produced at the rate of 5775 kg/h. This result determines the required heat duty for the steam superheater as 585 kW. 

Two problems (a) maximization of hydrogen and export steam flow rate, and (b) maximization of hydrogen and export steam flow rate, and minimization of total heat duty of the reformer. Oh et at. (2001) considered heat flux profile as a decision variable instead of furnace gas temperature in Rajesh et at. (2001). Oh et al. (2002b) optimized an indusUial hydrogen plant based on refinery off-gas. Oh a/.(2001) Oh /. (2002b)... 

Controlling the internal vapor flow to the section above the side draw Reboiler heat duty is measured and divided by the latent heat of the boiling mixture the measured side product flow is subtracted from the quotient to give the internal vapor rate in the section above the side draw. In a steam (or condensing vapor) reboiler, the internal vapor rate is computed as a constant times the measured steam rate less the measured side product flow, with the constant equal to the ratio of the latent heat of steam to that of the boiling mixture. An internal vapor controller (IVC) uses this computed internal vapor to manipulate product flow (Fig. 19.76). A limitation of this technique is that internal vapor is computed as a small difference between two large numbers and can therefore be in error. The error escalates as the internal vapor rate becomes a smaller fraction of the total vapor traffic below the side draw. 

A mixture of 60 mol% propylene and 40 mol% propane at a flow rate of 600 Ibmol/hr is distilled at 300 psia to produce a distillate of 99 mol% propylene and a bottoms of 95 mol% propane. The bottoms temperature is 138°F and the heat duty of the reboiler, Q, is 33,700,000 Btu/hr. When waste heat, consisting of saturated steam at 220°F, is used as the heating medium in the reboiler, estimate the area of a shell-and-tube reboiler. 

A kettle reboiler is used to evaporate toluene at 375°F with a heat duty of 3,000,000 Btu/hr. Steam is available at 50, 150, and 450 psig. Determine the steam pressure level to use, the steam flow rate in Ib/hr and Ib/yr, and estimate the annual steam cost if the plant-operating factor is 0.90. 

It is essential to avoid flooding and dumping, which could severely affect fractionation and thus energy efficiency. Fractionation efficiency can be monitored by column internal V/F ratios. Desired V/F can be achieved jointly by optimizing feed heater outlet temperature, fractionation stripping steam, and overhead reflux rate together with pump-around heat duties, which are used to control excess heat in the column. 

Steam reboiler duty and efficiency can be estimated directly from steam rates and conditions. We can also estimate furnace reboiler duty and efficiency. The amount of fuel fired in the reboiler can be measured from the meter. The heat delivered by fuel combustion can be estimated from both fuel rate and heating value of the fuel. 

Let s assume that we are generating 100,000 Ib/h of 150-psig steam. In the economizer section, the effluent from the deaerator, at 250°F, would be heated to 350°F. As the specific heat of water is 1.0 Btu/[(lb)(°F)], we would need 100 Btu/lb of water. However, to produce 100/100 lb of steam, we might need a 10 percent blowdown rate to control TDS. This means 110,000 Ib/h of boiler feedwater is needed. Therefore, the economizer heat duty would be... 

The statement that the mass, or weight flow of vapor through the trays, increases as the reflux rate is raised is based on the reboiler being on automatic temperature control. If the reboiler were on manual control, then the flow of steam and the reboiler heat duty would remain constant as the reflux rate was increased, and the... 

This would reduce the rate of steam condensation and also the reboiler heat duty. 

The heavy-duty jacketed type (Fig. ll-62a) is a special custom-built adaptation of a heavy-duty vibratory conveyor shown in Fig. 11-60. Its apphcation is continuously to cool the crushed materi [from about 177°C (350°F)] produced by the vibratoiy-type caster of Fig. 11-53. It does not have the liqmd dam and is made in longer lengths that employ L, switchback, and S arrangements on one floor. The capacity rate is 27,200 to 31,700 kg/h (30 to 35 tons/h) with heat-transfer coefficients in the order of 142 to 170 W/(m °C) [25 to 30 Btii/(h ft °F)]. For heating or drying applications, it employs steam to 414 kPa (60 IbFin ). 

This section covers system issues such as HHV, LHV, and cogeneration efficiency calculations, heat rate calculations, and cogeneration steam duty calculations. 

There are two ways to answer this question. Let s first look at the reboiler. As the tower-top temperature shown in Fig. 4.1 goes down, more of the lighter, lower-boiling-point alcohol is refluxed down the tower. The tower-bottom temperature begins to drop, and the steam flow to the reboiler is automatically increased by the action of the temperature recorder controller (TRC). As the steam flow to the reboiler increases, so does the reboiler duty (or energy injected into the tower in the form of heat). Almost all the reboiler heat or duty is converted to vaporization. We will prove this statement mathematically later in this chapter. The increased vapor leaving the reboiler then bubbles up through the trays, and hence the flow of vapor is seen to increase, as the reflux rate is raised. 

Let us assume that both the reflux rate and the overhead propane product rate are constant. This means that the total heat flow into the tower is constant. Or, the sum of the reboiler duty, plus the feed preheater duty, is constant. If the steam flow to the feed preheater is increased, then it follows that the reboiler duty will fall. How does this increase in feed preheat affect the flow of vapor through the trays and the fractionation efficiency of the trays ... 

It rather seems that 40 percent of the surface area of the radiator in Fig. 13.1 is submerged under water. If the water is drained out, does this mean that the rate of steam condensation will increase by the same 40 percent. Answer—yes Does this mean that the radiator heat transfer duty will increase by 40 percent Answer—not quite. 

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