Boiler operating line

SS/MA is very useful in cleaning boilers on-line that have been fouled as a result of out-of-control phosphate programs. It is a first-class polymer for operating phosphate programs with high FW hardness and voluminous amounts of sludge in the bulk BW. 

Another feature of boiler operations is the widely varying demands caused by changes in process operations, plant unit start-ups and shutdowns, and daily and seasonal cycles. Because utility equipment is often operated in parallel, demand swings commonly affect when another boiler, turbine, or other piece of equipment should be brought on line and which one it should be. 

Since the column consists solely of a rectifying section, there is a limit to how many trays can be profitably installed. The system will pinch regardless of stages once the low-boiler concentration in the reboiler approaches the intersection of the operating line with the equilibrium curve. 

The bottoms, however, becomes leaner xu2 < xbj. As overhead is withdrawn at higher and higher rales, a point is reached where the lower end of the operating line intersects the equilibrium line at yp (Condition 3). Here xaj and yp are equilibrium compositions. The overhead is still pure low-boiler, but there are two invariant zones, one at the bottom and one at the top of the column. 

And we define a function to optimize including the McCabe-Thiele method for the number of trays assuming constant relative volatility. We compute the operating lines as a function of the compositions of the feed, the distillate, and the residue. Next, we use a while statement to compute the number of theoretical trays. Finally, we compute the cost of the vessel and that of the energy required at the boiler. 

In natural circulation type boilers, the water system and steam system are divided by a steam drum. Boiler feedwater is preheated at the economizer and fed into a steam drum, then evaporated at the water wall (Evaporator) connected to the steam drum, before coming back to the steam drum as water-steam mixture. Water and steam are separated at the steam drum, then steam is led into superheaters and water is led into the water wall (Evaporator) again. Therefore, impurities of silica, etc., contained in boiler feedwater concentrates during boiler operation. The drum has a blow-down line to avoid concentration with a continuous blow-down to the... 

The smaller of the two boilers became short of water first, and the low w ater level trip shut it dowm. The operator was so busy trying to get it back on line that he ignored the low water level and other alarms that were sounding on the other boiler. Unfortunately the trips on this boiler did not work, as it had been rewired (incorrectly) since it was last checked. Fifteen to 20 minutes later, someone saw flames corning out of the boiler stack. The boiler was then shut down manually. By this time most of the tubes had melted. 

Steam lines from the boiler should always drain away from the boiler crown value to prevent condensate building up against the valve. Careless opening of this valve to allow steam to pass when the line is flooded can result in splitting the valve and pipework. If the steam line rises from the crown valve a tee trap must be installed and fitted with a steam trap and drain valve. The drain valve must be operated to check that the steam line is clear of water before the crown valve is opened. 

Blowdown from the boiler(s) should always be taken to either a blowdown sump or blowdown vessel before discharging into drains. Both should be adequately sized to give cooling by dilution and be fitted with vent pipes to dissipate pressure safely. The boiler(s) should have independent drain lines for the main manually operated blowdown valve and the drains from a continuous blowdown system. Where more than one boiler is connected to either system the line should be fitted with a check or secondary valve capable of being locked. 

Therefore, where a time clock is incorporated it is recommended that the crown valve(s) be closed at the end of each working day and only opened after the boiler has reached working pressure the next time it is required. This operation can be automated by the use of motorized or similar valves. These valves may be fitted to each steam, supply line from a manifold adjacent to the boilers and, provided adequate safeguards are incorporated to protect the boilers, the on-line boiler(s) may be left open to the manifold. Alternatively, each boiler may have its own automatic motorized start-up valve. Figure 23.12 illustrates a valve suitable for either system. 

Coil boilers can come on line quickly, providing full steam pressure within 5 to 10 minutes. This makes them particularly suitable for smaller batch operations and applications that require a rapid but intermittent steam demand. In addition, they can provide a backup in emergency situations. 

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