Blocked outlet

This contingency depends on the nature of the blocked outlet. A large number of scenarios are possible, and it is difficult to cover all these here. However, the contingency for major blocked-outlet scenarios can be estimated by the following procedure. 

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Blocked outlet. Operation or maintenance errors (especially following a plant turnaround) can block the outlet of a hquid or vapor stream from a piece of process equipment, resulting in an overpressure condition. 

Heat build-up Replace screen with one correctly sized and/or due to too fine or clean screen blocked outlet, Install pressure indicator downstream and screen. upstream of mill for conveyed systems Measure temperature at strategic points in mill casing to detect and alarm product temperature rise CCPS G-12 CCPS G-23 CCPS G-29... 

Running different products through mill, or change in upstream process, resulting in different feed characteristics and unsuitable milling conditions, e.g. overheating due to blocked outlet... 

The subheaders in each process area similarly will have two levels of flare headers. The line sizing of each level of subheader in an individual area will depend upon the maximum simultaneous flow in that particular area. Thus the line sizing criterion of a subheader may be the largest single flow due to a blocked outlet condition. This flow may not necessarily be the controlling load for the flare stack. 

Blocked Outlets on Vessels (a) For liquid, capacity is maximum pump-in rate, (b) For liquid-v apor system, capacity is total entering vapor plus any generated in vessel [10]. 

Blocked Outlets and Inlets for systems, lines or v essels, capable of being filled with liquid and heated by the sun or process heat, require thermal relief to accommodate the liquid expansion (assuming vaporization is negligible). 

Consider constant flow into protected equipment (blocked outlet). For the steady-state design scenario with a constant flow of fluid Win (kg/s) from a pressure source that is above the maximum allowed pressure in the protected equipment, volume is being generated within the equipment at a rate of Win/pin, where pin (kg/m3) is the incoming fluid density evaluated at the maximum allowed pressure. Denoting pout (kg/m3) as the vent stream fluid density, Eq. (23-89)... 

Together with the blocked outlet case, external fire cases are probably one of the most common cases where SRVs are required within the modem process industry. 

Due to the variety of blocked outlet situations, different methods were used to determine the required relief rates for different types of equipment. The quantity of the material to be relieved was generally determined at the relieving conditions (i.e. the MAWP plus the code-allowable overpressure) based on the capacity of upstream pressure sources or duty of process heaters. 

Blocked outlet Utility failure Cooling or reflux failure Inadvertent valve opening Loss of fans... 

If the temperature is constant (which is valid for a blocked outlet relief scenario). 

Estimate the relieving load for the reactor designed in Problem 13.7 for a blocked outlet scenario and size the relief valve for this case. 

Furthermore, significant power in excess of normal running requirements causes other problems. In the case of an overload, such as the outlet of the machine becoming blocked, surplus power installed to overcome a starting load dispersed over the length of the feeder will be concentrated upon the final screw flight that is delivering material up to the blocked outlet. 

The usual consequence of a blocked outlet is to cause costly damage to the screw flights or to some component of the drive. This can happen quite quickly but take some time to repair, so it is good insurance to ensure this prospect is avoided. A hinged flap above the outlet fitted with a safety... 

Blocked outlet 2) inadvertent valve open 3) control valve failure (full open or close) 4) loss cooling stream 5) instrument aii failure 6) power failure 7) abnomiaJ heat input 8) equipment failure 9) heat exchanger tube ruphue ID) thermal expansion 11) fire 12) chemical reaction 13) steam out, 14) operator error, etc. 

Blocked-outlet pressure protection may be required because of overpressure by pumps or compressors. The following general guidelines should be used to establish the protection requirement and contingency ... 

Blocked-outlet relief is possible even in a multioutlet case. The following general guidelines will apply ... 

Multiple outlet blockage should be considered if the blocked outlet is caused by operator intervention and the same logic causes multiple outlet blockage. 

In a single or multiple blocked-outlet situation, the inlet valve is considered at its normal operating position unless the blocked situation itself alters the position of the inlet valve. 

Block valve downstream of control valve In this situation, the following methodology is used to establish the blocked-outlet contingency ... 

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