Existing Plants

In any case, the prevatiing ideas of nuclear safety were not substantiated by these figures. Therefore, responsible people started to think about the best way severe accidents could be prevented, or at least mitigated. The Three MUe Island event reinforced and confirmed this need for progress in nuclear safety. 

Although none of the Rasmussen report sequences replicated exactly the course of events in TMI, the report sequence TMLB was rather close to what happened there. TMI was certainly a severe accident, even if the degree of devastation suffered by the core was not clear from the start. 

TMI was a real shock for all in the nuclear industry. Many, dubious that the efforts made for nuclear safety were really needed, were indeed struck by the new evidence human errors, communication 

It is true that the foresighted adoption of Defence in Depth provisions at TMI prevented any casualties. It can be recalled that only 666 GBq (18 Ci) of iodine were released to the environment, with a correspondingly minute virtual dose at the fence of 0.8 mSv. 

Besides the post-TMl plant improvement programmes (prevention) which cost millions of dollars for each plant, in the Western countries investigations were started on what else could reasonably be done to the plants with the goal of stopping the progression of an impending severe accident or to mitigate its consequences. 

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Conceptual Design of MHD Repowered Plant. The first step toward MHD plant commercialization is a pilot-scale demonstration plant. Repowering of existing plants, actively under study both in the United States and elsewhere (65), allows use of existing systems at considerable cost savings compared to building a new plant from the ground up. It also ensures that the pilot scale demonstration occurs in a reaHstic utiHty environment and... 

Research nd Development. Eor commodity chemicals, emphasis is on the improvement of plant operation and reduction of production costs. Eor specialty chemicals, emphasis is on assembling a staff capable of quickly identifying and solving a customer problem under the existing plant conditions and operating procedures of the customer. 

Some of the earlier BWR units had feedwater heaters having copper alloy tubes. The environment of high oxygen and neutral pH water led to high copper concentrations in the feedwater and to undesirable deposits on the fuel and inlet fuel nozzles (20). In some instances, the copper deposits resulted in an increase in core pressure drop and necessitated plant power reduction. The copper alloys were eliniinated from the feedwater system in subsequent plants and most existing plants. 

Other factors that affect either production cost or the consumption of fertilisers tend to be periodic and short-Hved. On the consumption side, weather conditions, prices of fertilisers, and the pohtical stabiUty of a region influence demand. The supply side is influenced by raw material availabihty, rehabihty of infrastmcture, on-stream efficiency, age of plants, and the constmction or modernisation of existing plants. 

Good design ideas for new plants are also good for existing plants, but there are three basic differences. (/) Because a plant already exists, the capital—operating cost curve differs. Usually, this makes it more difficult to reduce utiHty costs to as low a level as in a new plant. (2) The real economic justification for change is more likely to be obscured by the plant accounting system and other nontechnical inputs. (2) The real process needs are... 

Catalytic uses result in Htde consumption or loss of vanadium. The need to increase conversion efficiency for pollution control from sulfuric acid plants, which require more catalyst, and expanded fertilizer needs, which require more acid plants, were factors in the growth of vanadium catalyst requirements during the mid-1970s. Use was about evenly divided between initial charges to new plants and replacements or addition to existing plants. 

The fluidized-bed bioreactor (FBBT) (26) increases the capacity of existing plants. Primary effluent is passed upward through the columnar reactor filled with sand or carbon with sufficient velocity to fluidize the bed. An attached biomass develops on the bed particles. Intimate contact between the biomass and waste is provided and improved removals are reported. Oxygen is provided by a deep U-tube reactor. No biomass recirculation is required and a secondary clarifier is not necessary. 

Energy Related Applications. Much research, with regard to the use of cesium in energy related processes, has resulted in Httle commercial apphcation. The heightened awareness of the environmental degradation caused by fossil fuel power stations has resulted in increased research both into efficiency improvements for existing plants and into alternative power generation (qv) methods. 

The project may be a complete plant, an addition to an existing plant, or a plant modification. 

Facilities Reviews There are many lands of facilities reviews that are useful in detec ting and preventing process safety problems. They include pre-start-up reviews (before the plant operates), new-plant reviews (the plant has started, but is stiU new), reviews of existing plants (safety, technology, and operations audits and reviews), management reviews, critical instrument reviews, and hazardous materials transportation reviews. 

Controlled catalyst circulation is one of the most important prerequisites for trouble-free operation of the FCC unit. Uniform circulation is ensured by controlling the differential pressure between the reactor and regenerator. The differential pressure in the existing plant is controlled by a differential pressure governor adjusting the position of the double slide valve upstream of the orifice chamber. 

Flare Systems. There is a good chance that the operating company will not have anyone experienced in flare system design. For feasibility cost estimates, rough estimates can be made by comparison with existing plants or a vendor can be contacted for budget cost estimates for the flare stacks and associated knockout drum, burner tip, igniter, and molecular seal. 

The applicable code procedures should be followed, particularly in regard to instrumentation. On an existing plant, this will require planning in advance of a scheduled shutdown. The pressure and temperature tap locations and installation details can all be developed with the compressor running. All details must be followed. When a drawing states, deburr, do not chamfer that is exactly what it means (see Figure 10-7). 

New low-NO, burners are effective in reducing emissions from both new power plants and existing plants that are being retrofitted. Low NO, burners limit the formation of nitrogen oxides by controlling the mixing of fuel and air, in effect... 

Catalytic crackings operations have been simulated by mathematical models, with the aid of computers. The computer programs are the end result of a very extensive research effort in pilot and bench scale units. Many sets of calculations are carried out to optimize design of new units, operation of existing plants, choice of feedstocks, and other variables subject to control. A background knowledge of the correlations used in the "black box" helps to make such studies more effective. 

Increased Plant Capacity - When an existing plant capacity is increased, the entire pressure relieving system should be reevaluated, even though new equipment has been added. For example, a unit operating at 120 % of design capacity may require additional pressure relieving capacity. 

In an existing plant, the team should include several people with experience of the plant. A typical team comprises ... 

Transportation should be considered when assessing risks associated with planned or existing plants. The design of new chemical processing units should include at the earliest opportunity a qualitative or quantitative risk assessment of the whole system including production, use, and transportation in order to minimize overall risk. A brief discussion of the inherent safety aspects of transportation is included in Chapter 5. 

During process hazard reviews, evaluate each safety critical device or procedure to see if the device or procedure can be eliminated by applying inherently safer principles. Consider the existing plant, the next plant, and the plant after next. 

In addition to the hazardous waste standards, there may be a variety of other standards that may apply to any worksite. One standard that seems to surprise PMs is the lead standard. Even projeets that are elean eonstruetion (not HAZWOPER or working with ehemieals) may eome under the lead standard. If new proeess equipment is being installed in an existing plant, any tie-ins, pipe raek, struetural members, and even walls may have been eovered with many layers of lead-based paint. 

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