System Ring-main

There are two main types of oil-handling system in common use. These are gravity and ring main. 

Ring main systems are of three types hot oil, warm oil and cold oil. Hot oil ring mains circulate oil at atomizing temperature, warm oil ring mains at a temperature between minimum pumping and atomizing temperature, and cold oil ring mains at ambient temperature. 

This system is similar to a cold oil ring main but includes provision for heaters in the circuit to maintain oil temperature between minimum handling and atomizing levels. This provides a reduction in oil viscosity and reduces pipe friction. The circulation temperature of the oil should... 

Pressure drop under streamline flow conditions is directly proportional to the quantity of oil flowing. The effect of reduced flow rate after take-off points, as compared with full flow rate throughout the full length of the pipeline when there is no take-off, should be taken into account to ensure that variation in pressure is within the specified pump output. Special consideration is necessary with gravity and ring main systems serving several take-off points. 

It is clear from the foregoing that ring closure to five-membered rings fused to the isoxazolidine, regardless whether part of a pyrrolizidine or of an indolizidine system, led mainly to the cis-anti isomers (see 243 a, b and 246 a, b)... 

Hydrants should be considered as a backup water supply source to monitors and fixed fire suppression systems. Hydrants should be located on the ring main at intervals to suitably direct water on the fire hazard with a fire hose. Hydrants monitors and hose reels should be placed a minimum of 15 meters (50 ft.) from the hazard they protect for onshore facilities. Hydrants in process areas should be located so that any portion of a process unit can be reached from at least two opposite directions with the use of 76 meters (250 ft), hose lines if the approach is made from the upwind side of the fire. Offshore hydrants are located at the main accessways at the edge of the platform for each module. Normal access into a location should not be impeded by the placement of monitors or hydrants. This is especially important for heavy crane access during maintenance and turnaround activities. 

Camptothecin (Figure 6.93) from Camptotheca acuminata (Nyssaceae) is a further example of a quinoline-containing structure that is actually derived by modification of an indole system. The main rearrangement process is that the original (>-carboline 6-5-6 ring system becomes a 6-6-5 pyrroloquinoline by ring expansion of the indole... 

The intramolecular addition of organolithiums to non-activated carbon-carbon double or triple bonds has now become an efficient way of constructing carbocyclic and heterocyclic systems. Although mainly confined to the formation of five-membered rings, the high regio- and stereoselectivity of these reactions and the possible functionalization of the... 

The indole alkaloids so far discussed all have a tetrahydro-/ -carboline system. The main fragments of these alkaloids contain the indole part of the molecules. This situation is changed in alkaloids which have a larger ring C or an indoline system, permitting the production of fragments characteristic of both the indole and piperidine moieties. 

Only few examples were reported related to these ring systems. Moreover, only those fused with three-membered ring mainly containing one heteroatom oxygen were reported. No examples can be found with a four-membered ring containing two heteroatoms. 

For the S-1 oxide of (10) the S=0 bond is in an equatorial orientation, and the bond lengths, and bond angles, are similar to the parent system. The main structural differences are a slight contraction of the ring angles at C and at the oxidized S and an expansion at the adjacent N... 

This chapter has been split into two main sections. The first deals with monocyclic compounds and the second deals with compounds containing more than one ring, mainly benzo-fused ring systems. 

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