Reboilers specifications

Condenser and eboiler AT. The losses for AT are typically far greater than those for reflux beyond the minimum. The economic optimum for temperature differential is usually under 15°C, in contrast to the values of over 50°C often used in the past. This is probably the biggest opportunity for improvement in the practice of distillation. A specific example is the replacement of direct-fired reboilers with steam (qv) heat. 

Stressed, such as heat-affected zones near welds, in areas of high acid-gas concentration, or at a hot gas-liquid interface. Therefore, stress-relieving all equipment after manufacturing is necessary to reduce corrosion, and special metallurgy in specific areas such as the still overhead or the reboiler tubes may be required. 

For most field gas units it is not necessary to specify a stripper size. Vendors have standard design amine circulation packages for a given amine circulation rate, acid-gas loading, and reboiler. These concepts can be used in a preliminary check of the vendor s design. However, lor detailed design and specification of large units, a process simulation computer model should be used. 

Vo = specific volume of fluid at outlet of reboiler, fE/lb Vi = specific volume of fluid at inlet to reboiler, fE/lb log = log base 10... 

The plant has a spare kettle reboiler available with the following specification. U-tube bundle, 50 tubes, mean length 4.8 m, end to end. 

A column of four stages exists analogous to that shown in Figure El2.1 except that more than one feed can exist (the reboiler is stage 1 and the condenser is stage 4). Feed and product specifications are... 

Figure 11.5a shows a typical implementation of feedforward controller. A distillation column provides the specific example. Steam flow to the reboiler is ratioed to the feed flow rate. The feedforward controller gain is set in the ratio device. The dynamic elements of the feedforward controller are provided by the lead-lag unit. 

Any reboiler is calculated in the subroutine written specifically for this purpose. The subroutine first checks the variable flfees which is the total mass input to the reboiler. If flfees is zero, the exit streams from the reboiler are set to zero, it is noted that the problem has been altered, and the calculation returns to the basic program. 

The specific gravity of the liquid in the reboiler feed line is 0.600. 

The mixed-phase specific gravity of the froth leaving the reboiler is 0.061. 

Increasing the steam or hot-oil flow through the reboiler. This reduces the specific gravity or density of the froth or foam in the reboiler effluent line. 

Regardless of the type of reboiler used, the tower bottom product temperature has to be the same, so as to make product specifications. This is shown in Fig. 5.5. However, the reboiler outlet temperature must always be higher in the circulating reboiler than in the once-through reboiler. This means that it is more difficult to transfer heat in the former than in the latter. 

Formulation of the mathematical model here adopts the usual assumptions of equimolar overflow, constant relative volatility, total condenser, and partial reboiler. Binary variables denote the existence of trays in the column, and their sum is the number of trays N. Continuous variables represent the liquid flow rates Li and compositions xj, vapor flow rates Vi and compositions yi, the reflux Ri and vapor boilup VBi, and the column diameter Di. The equations governing the model include material and component balances around each tray, thermodynamic relations between vapor and liquid phase compositions, and the column diameter calculation based on vapor flow rate. Additional logical constraints ensure that reflux and vapor boilup enter only on one tray and that the trays are arranged sequentially (so trays cannot be skipped). Also included are the product specifications. Under the assumptions made in this example, neither the temperature nor the pressure is an explicit variable, although they could easily be included if energy balances are required. A minimum and maximum number of trays can also be imposed on the problem. 

Of these, the feed mixture may or may not vary, but is generally taken as given. The column pressure and the degree of subcooling are normally fairly constant. The main operational variables are the reflux ratio R and the heat input to the reboiler QR and once these are set, the amount of product withdrawal at the bottom or at the top will also be given by the product specifications. An optimum exists for the reflux ratio in terms of operating costs, and normally a number of ratios are tested, and the economics of each scenario is investigated, before a decision is reached. 

Under the above modeling assumptions, the dynamic model of the reactor-column-recycle system consists of the material balance for the total molar holdup of the reactor, condenser, and reboiler, and component-wise balances for the reactant A and product Pi in the reactor, condenser, reboiler, and column trays, having a total of 2N + 9 differential equations. Specifically,... 

---