Fire case

Unfired cycle This cycle is very similar to the mentary-fired case except there is no added fuel heat input. The approach temperature and pinch point are even more critical, and tend to reduce steam pressures somewhat. Similarly, the gas turbine exhaust temperature imposes further limits on final steam temperature. 

The catalyst storage tank failed earlier than expected if the fireproofing insulation was in good condition and the relief valve was adequate for the fire case. Witnesses indicate that several sections of the insulation had either fallen off or heen removed from the tank 2-3 months ago. The insulation had not heen repaired. (Mechanical integrity)... 

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. 

Sub-paragraph (c) (2) covers a fire case. Again, capacity certification is based only on the set pressure of the SRV and is unrelated to MAWP, unless of course the set pressure is MAWP. 

Where PRDs normally sized (except fire case where it is 21%)... 

Protection with ONE safety relief valve Fire case 21% of MAWP... 

Note To emphasize the difference between overpressure (safety relief valve characteristic) and accu-mulation (code limitation on the pressure vessel), safety relief valves installed for fire cases will have an overpressure of 10% like most safety relief valves, even if the allowed accumulation on the pressure vessel is 21% in the case of ASME VIII. ... 

PED 97/23/EC Protection with ONE SRV Case Fire case Setting of SRV Below or at MAP Accumulation 10% above MAP or higher if proved safe by the vessel designer... 

Protection with MULTIPLE Fire case One valve below or at MAP and 10% above MAP or higher if... 

For fire case, basically the PED does not dictate any particular accumulation, and this must be reviewed by the designer of the pressure equipment and this engages his/her responsibility. This should not exclusively be decided by the safety valve characteristics, manufacturer or the user. 

E. ASME VII - LIG-125 Accumulation of vessel above MAWP for process and fire case is 21% (Figure 4.5). 

For example, API 521 for fire case calculations basically allows you to ignore heights above a certain height when considering how much vessel surface to include in a fire zone calculation (see Section 2.3.2). Some companies go up to 8 m while others go up to 30 m for fire sizing and others simply have no height limit, considering that for a fire in a tank farm, for instance, it has been demonsttated that flames can reach over 100 m. 

For fire case applications where 21% overpressure is allowed Kb = 1 may be used up to a backpressure of 50%. 

For some relief scenarios, correlations have been established for the relieving load. For the external fire case, API RP 521 (Section 3.15.2) gives... 

Rupture disks are often used upstream of relief valves to protect the relief valve from corrosion or to reduce losses due to relief valve leakage. Large rupture disks are also used in situations that require very fast response time or high relieving load (for example, reactor runaway and external fire cases). They are also used in situations in which pressure is intentionally reduced below the operating pressure for safety reasons. 

So the external fire case has the higher relieving load and governs the design. If the vent line discharges to a flare system at atmospheric pressure, then... 

Fire case relieving mass flow rate... 

A toluene surge drum has capacity 500 gal and is normally operated 60% full at 100°E under 300psig of hydrogen in the head space using a level-controlled outflow The normal flow rate into the vessel is 30,000 Ib/h. Determine the vessel dimensions if the vessel is vertically mounted. Evaluate the relief loads for the blocked outflow and external fire cases and hence determine the relief valve size. 

Fire codes or standards have governed urethane business for some time and have played a prominent role in the creation of building codes. Unfortunately, fire statistics currently are based on a minimum number of collected fire cases which become the base for regulatory activity that impacts industry and consumers. 

Figure 12.4 shows the use of fire zones. A ring main goes around the entire facility. It is filled with water whose pressure is maintained with a jockey pump. Connected to the ring main are multiple zones. The fire water headers in each zone are normally dry. In this example, there are two fire water pumps, each of which has sufficient capacity on its own to handle the design fire case. These pumps are placed in different locations at the facility so that, if one is destroyed, the other will provide a full flow of fire water. It is common for them to have different power supplies—in particular, one of them will be driven by a stand-alone diesel motor that operates independently of the facility s utility systems. 

Install new process drums/vessels so that they are away from the fire circle that is generating maximum relief during fire case scenario... 

New process equipment installed within 7.6 meters from the grade/ground level will require pressure relief devices due to fire scenario. For revamp cases, it may be advantageous to place vessels on platforms at >7.6 meters if fire case relief load is most credible and bottlenecks the existing flare system. Fire circle or zone is defined as the maximum affected area during any equipment fire in the facility. API 521 (2014) defines its area as 230 to 460 m. Addition of process equipment inside an existing fire circle may increase the fire circle size. Hence, care shall be taken to review the fire circle size with each equipment addition. It will impact the peak relief load during the fire scenario. 

Thermal expansion and fire cases are not required to be checked, if the existing equipment is re-used, with the same service and also the same level control setting. Overpressure relief requirements due to each utility failure, fire cases and any other combination scenarios need to be estimated. API 521 (2014) has a comprehensive list of effects for utilities failure. All the PRV manifolds shall be checked to estimate back pressures at the PRVs. PRD overpressure calculations for equipment shall be documented as shown in Table 3.4. Vacuum relief (if the vessel/s is/are not designed to withstand full vacuum) shall also be documented. All the flare scenarios and flare network shall be properly documented. An example of PRV sizing calculations for the system shown in Figure 3.5 is presented in Table 3.4. 

Thermal oxidation is a widely used route and the resultant energy is available to be utilised to save fuel and hence energy costs. A particularly efficient option is use of spent solvent as a fuel for cement manufacture, where it offers an attractive alternative to the practice of burning powdered coal. This combines a second use of the solvent molecules, with a net reduction in environmental emission compared to the coal fired case. 

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