Tank liquid level

Assume tank liquid level is 10 feet above center line of pump, then S = -HIO feet. 

Large storage tanks need a breather vent (technically called a conservation vent) to allow air to move into and out of the tank as a result of temperature and pressure changes and a change in the tank liquid level. Unfortunately, these vents also allow volatile materials to escape, resulting in potential worker exposures. 

Apply a volume adjustment to the results of step 3. Since geometric similarity scaleup resulted in a volume of only 4444 gal (16.8 m3) in a 120-in (3.05-m) diameter tank and the design specification called for 7000 gal (26.5 m3) a higher liquid level is required. Based on the calculations in step 1, the open-tank liquid level would be 99.1 in (2.52 m). Allowing 10% for internals, the actual liquid level will be about 109 in (2.77 m). 

GUARANTEE This unit will give full capacity with tank liquid level 2 Ft. or more above ui ... 

Building up a model of a simple process-plant unit tank liquid level... 

The variables used in the model of the tank liquid level system above may be characterized as in the Table 2.1. 

To demonstrate this, let us consider our example, the tank liquid level system of Figure 2.1. 

It will be appreciated that our description of the plant is, in reality, only an approximation covering as few features as we can get away with, while still capturing the essential behaviour of the plant. For instance, in the example above of the tank liquid level, no mention was made of liquid temperature, entailing an implicit assumption that temperature variations would be small over the period of interest. If it had been necessary to allow for temperature effects, perhaps because of fear of excessive evaporation or because of environmental temperature limits set for a waste water stream, then liquid temperature would have had to be included as an additional state variable, and the dimension or order of the plant as we modelled it would go up from 4 to 5. If we had needed to make an allowance for the temperature of the metal in the tank. 

To put some flesh on these theoretical bones, let us consider again the tank liquid level system. Linearization of the equation set (2.21) allows us to set down the Jacobian matrix in terms of the states and the system... 

Tabl 2.2 Operating point data for the tank liquid level system... 

It is thus apparent from the simple but quite feasible example of the tank liquid level system that stiffness can easily become a significant feature of the simulation of a process plant. While stiffness in such a small simulation as this will not cause a major computational burden, stiffness in a larger process plant system will result in a very significant slowing of the integration, and special measures need to be taken to counter its influence. 

When the condenser and condensate tank are closely connected, the condensate tank must be properly sized in order to permit the condensate liquid level to be controlled somewhere in the condensate tank. If the condensate tank is too small, liquid level control can be achieved only by flooding part of the condenser, especially when the condensate is pumped from the tank. Liquid level must be maintained in the condensate tank and not in the condenser. 

A pump moves a fluid (p = 1180 kg/m p = 0.0012 pascal-sec) from the bottom of a supply tank to the bottom of a hold tank. Liquid level in the hold tank is 60 m above that in the supply tank. The pipeline (0.15-m diameter 210-m length) connecting the tanks contains two gate valves and four elbows. If the flow rate is to be 0.051 m/sec, what is the cost to run the pump for one day Energy cost is one dollar per HP-day. 

The differences between the updated model and data are plotted in Figure 12.13. As shown, the slope in difference between data and model is effectively accounted for, that there is a small remaining residual difference between data and model, and that the model now predicts slightly better performance than the data. There are two primary reasons for this residual difference. The first has to deal with the way the velocity profile transitions from the submerged channel portion to the exposed channel portion in the model. The velocity profile in the channel has a significant Vy component at the location just below the L/V interface level of the tank, as shown in Figure 12.14. The model assumes that immediately after the liquid in the channel has passed the tank liquid level, the flow is fully... 

Consider a single tank liquid-level system where the outflow passes through a valve. Recalling Eq. 2-56, assume now that the valve discharge rate is related to the square root of liquid level ... 

Before and after each test, measurements were made of the tank liquid level (with a movable thermocouple probe) and of the pressure in the pressurizing-gas manifold. These were the only measurements made outside the control center. The general procedure for testingwas as follows the tank was pressurized to the desired level by manual operation of the ullage pressure control valve liquid transfer was initiated approximately 1 to 9 min after the tank was pressurized the tank pressure during the hold and transfer periods was maintained constant. 

The problem of distillation control was addressed in Chapter 8. The issue now is how to control the reactor liquid level, the recycle tank liquid level, the recycle flow rate, the ethylene oxide feed flow rate, and the water feed flow rate. 

In Equations W2.1 and W2.2, SI units are flow in m /h and head in metres. Use the spreadsheet unit operation to incorporate Equations W2.1 and W2.2 into the simulation. Import the tank liquid level into the spreadsheet, assume a tank geometry, and use the resulting value of head to calculate the liquid outlet flow. A K value of 0.4 should work well with these units. Then export the calculated flow back to the worksheet as the... 

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