Blowouts

The existence of multiple steady states for a CSTR gives rise to several interesting and important phenomena, two of which are known as blowout and feed-temperature hysteresis. 

Suppose that the volumetric flow rate to the reactor described above is increased by 20%, with no change in die feed concentrations. A new steady state then is allowed to establish. At what tenqierature and fractional conversion does the CSTR operate, at this new steady state  

The average residence time, r, has decreased as a result of the increase in the voliunetric feed rate. Therefore, the conversion of A, xa, will decrease, at a fixed tenqrerature, leading to a new G(T) curve. The location of this ciuve will be calculated and Gnew(T) will be plotted versus T. 

Even diough the feed temperature (To) remains constant, the increase in feed rate will cause 

Hie 20% increase in feed rate has effectively extinguished, or blown out the reaction. The conversion of A has dropped horn about 84% to almost 0, and the reactor temperature has dropped from about 453 K to about 312 K. 

---

Semi-submersible rigs are often referred to as semis , and are a floating type of rig. Like the jack-up, a semi is self contained. The structure is supported by large pontoons which are ballasted with water to provide the required stability and height. The rig is held in position by anchors and mooring lines or dynamically positioned by thrusters. A large diameter steel pipe ( riser ) is connected to the sea-bed and serves as a conduit for the drill string. The blowout preventer (BOP) is also located at the sea-bed ( sub sea stack ). 

An important safety feature on every modern rig is the blowout preventer (BOP). As discussed earlier on, one of the purposes of the drilling mud is to provide a hydrostatic head of fluid to counterbalance the pore pressure of fluids in permeable formations. However, for a variety of reasons (see section 3.6 Drilling Problems ) the well may kick , i.e. formation fluids may enter the wellbore, upsetting the balance of the system, pushing mud out of the hole, and exposing the upper part of the hole and equipment to the higher pressures of the deep subsurface. If left uncontrolled, this can lead to a blowout, a situation where formation fluids flow to the surface in an uncontrolled manner. 

Blowout preventers are opened and closed by hydraulic fluid stored under a pressure of 3000 psi in an accumulator, often referred to as a Coomy unit. 

The casing will also carry the blowout preventers described earlier. 

In the event of a sudden loss of mud In an Interval containing overpressures the mud column in the annulus will drop, thereby reducing the hydrostatic head acting on the formation to the point where formation pressure exceeds mud pressure. Formation fluids (oil, gas or water) can now enter the borehole and travel upwards. In the process the gas will expand considerably but will maintain its initial pressure. The last line of defence leff is the blowout preventer. However, although the BOP will prevent fluid or gas escape to the surface, closing in the well may lead to two potentially disastrous situations ... 

Formation breakdown (fracture development) In a shallower, weaker formation and subsequent uncontrolled flow from the deeper to the shallower formation (internal blowout). 

Formation breakdown and subsequent liquefaction of the near surface strata and the initiation of cratering below the rig. This will result in a surface blowout... 

Two suppliers to the U.S. market are Bayer and Nippon Zeon. The estimated volume used in the United States is 500 700 t/yr. Hydrogenated nitrile mbber (HSN or HNBR) compounds compete with EKM, EVMQ, ECO, ACM, and high ACN content nitrile mbbers. Big applications include automotive timing belts, blowout preventors, drill pipe protectors, and numerous oil and fuel pump components. 

The spiral-wound type furnished with a sohd metallic ring on the outside to hmit gasket compression provides protection against blowout when used with raised facing. 

The explosion and fire (May 1,1990) caused eight deaths (including a vice-president and site manager), 120 injuries, extensive damage to buildings in the area, and evacuation of an entire small town. The cause of the explosion, at the Angus Chemicals Plant, was the blowout of a compressor line on the nitroparaffin unit. 

Water enters MIC Refriger- ation P. relief valve- blowout Scrub- Flare bar 1 stack... 

It generally is recommended, and often required, that gas dcicciiuii systems be installed in a fail-safe manner. That is, if power is disconnected or otherwise interrupted, alarm and/or process equipment shutdown (or other corrective action) should occur. All specific systems should be carefully reviewed, however, to ensure that non-anticipated equipment shutdowns would not result in a more hazardous condition tlian the lack of shutdown of the equipment. If a more hazardous situation would occur with shutdown, only a warning should be provided. As an example, a more hazardous situation might occur if blowout preventers were automatically actuated during drilling operations upon detection of low levels of gas concentrations than if drilling personnel were only warned. 

Figure 5.10 shows a detailed fault tree for an offshore drilling operation. The top event of the fault tree is Failure to use shear rams to prevent blowout. As wi the fault tree in Figure 5.2, the representahon combines both hardware... 

FIGURE 5.10. OfEshore drilling blowout fault tree subtree. 

FIGURE 5.10. Offshore Drilling Blowout Fault Tree Subtree, "Fail to use shear rams to prevent blowout." 221... 

The commercial recovery of iodine on an industrial scale depends on the particular source of the element.Erom natural brines, such as those at Midland (Michigan) or in Russia or Japan, chlorine oxidation followed by air blowout as for bromine (above) is much used, the final purification being by resublimation. Alternatively the brine, after clarification, can be treated with just sufficient AgNOs to precipitate the Agl which is then treated with clean scrap iron or steel to form metallic Ag and a solution of EeU the Ag is redissolved in HNO3 for recycling and the solution is treated with CI2 to liberate the h ... 

After the surface casing has been tested and the blowout preventer installed, drilling operations are resumed. They will continue until the well has been drilled to the total depth decided upon. Usually the... 

Add weighting material to rise density. Thin mud with water and thinners. Use degasser to clear gas from mud. Continue to circulate and avoid use of blowout preventers if possible. 

High Pressure. Limestones. Blowout prevention. Maintain adequate mud density. Maintain hole full of mud to prevent reduced hydrostatic head resulting from short column of mud. 

---