Operator, delta

A typical 20-MW, a-c furnace is fitted with three 45-in. (114.3-cm) prebaked amorphous carbon electrodes equdateraHy spaced, operating on a three-phase delta connection. The spacing of the electrodes is designed to provide a single reaction zone between the three electrodes. The furnace is rotated to give one revolution in two to four days or it may be oscillated only. Rotation of the furnace relative to the electrodes minimizes silicon carbide buildup in the furnace. 

This method is applicable to single-star or delta-connected capacitor banks. Unbalance can be detected through the use of an RVT (residual voltage transformer) (Section 15.4.3). See Figure 26.4. The theory of operation is that any unbalance, of the system or the capacitor bank, will shift the neutral and reflect as the residual voltage across the open delta and can be used for the protective scheme. The unbalance voltage across the open delta in the event of failure of a unit in any series group can be expressed by... 

While working in a plant, a troubleshooter read a pressure gauge daily for several weeks and only realized it was inaccurate when one day the blower was down. The gauge still read about normal operating pressure. Had this have been a distillation unit, it could have been more serious. In distillation service, pressure is a more important variable than in many other unit operations. Relative volatility is a function of pressure. Pressure, or more accurately delta-P, is the best indication of the tower hydraulics. 

An additional series of process tests and plots can be helpful. The Delta-P over each section should be monitored and the reflux increased/decreased at constant bottom temperature. The composition of the heavy key in the overhead should be monitored. Plots should then be made of both Delta-P and of composition vs. reflux. Additional information concerning these tests can be found in Norman Lieberman s book entitled Troubleshooting Process Operations. ... 

The Rijnmond area is that part of the Rhine delta between Rotterdam and the North Sea. The Commission for the Safety of the Population at large (COVO) commissioned the study for six chemicals and the operations associated with them acrylonitrile, liquid ammonia, liquid chlorine, LNG, propylene, and part of a separation process (diethanolamine stripper of a hydrodesulfurizer). The study objectives were to evaluate methods of risk assessment and obtain experience with practical applications of these methods. The results were to be used to decide to what extent such methods can be used in formulating safety policy. The study was not concerned with the acceptability of risk or the acceptability of risk reducing measures. 

A completely different type of property is for example spin-spin coupling constants, which contain interactions of electronic and nuclear spins. One of the operators is a delta function (Fermi-Contact, eq. (10.78)), which measures the quality of the wave function at a single point, the nuclear position. Since Gaussian functions have an incorrect behaviour at the nucleus (zero derivative compared with the cusp displayed by an exponential function), this requires addition of a number of very tight functions (large exponents) in order to predict coupling constants accurately. ... 

Using the operating data from the case study. Example 5-5 shows heat balance calculations around the stripper-regenerator. The results are used to determine the catalyst circulation rate and the delta coke. Delta coke is the difference between coke on the spent catalyst and coke on the regenerated catalyst. 

The heat balance exercise provides a tool for in-depth analysis of the unit operation. Heat balance surveys determine catalyst circulation rate, delta coke, and heat of reaction. The procedures described in this chapter can be easily programmed into a spreadsheet program to calculate the balances on a routine basis. 

Many factors influence delta coke, including quality of the FCC feedstock, design of the feed/catalyst injection system, riser design, operating conditions, and catalyst type. The following is a brief discussion of these factors ... 

Reactor stripper. Operational and hardware changes to the stripper improve its performance by removing the entrained and adsorbed hydrocarbons. The benefits are lower delta coke and more liquid products. 

The unit operating philosophy and its apparent operating limits often dictate unit constraints. For example, limitations on the main column bottoms temperature, the flue gas excess oxygen, and the slide valve delta P often constrain the unit feed rate and/or conversion. Unfortunately, some of these limits may no longer be applicable and should be reexamined. Some of them may have resulted from one bad experience and should not have become part of the operating procedure. 

---