Start up rate

Figure 4-6 shows the typical trend of the start-up rate, expressed in decades of growth of the neutron flux per minute, as a function of reactivity. The relationship connecting the start-up rate to the period T (s) is ... 

Rates for rod withdrawal and boron reduction are specified in such a way that the start-up rate is less than one decade per minute. 

D) One could use other relations, such as decades-per-minute (DPM), called start-up rate (SUR). SUR is often used to express power rate-of-change at PWR facilities. SUR can be related to period ... 

For the example above calculate reactor period, T, and start-up rate, SUR. 

Control of the core is affected by movable control rods which contain neutron absorbers soluble neutron absorbers ia the coolant, called chemical shim fixed burnable neutron absorbers and the intrinsic feature of negative reactivity coefficients. Gross changes ia fission reaction rates, as well as start-up and shutdown of the fission reactions, are effected by the control rods. In a typical PWR, ca 90 control rods are used. These, iaserted from the top of the core, contain strong neutron absorbers such as boron, cadmium, or hafnium, and are made up of a cadmium—iadium—silver alloy, clad ia stainless steel. The movement of the control rods is governed remotely by an operator ia the control room. Safety circuitry automatically iaserts the rods ia the event of an abnormal power or reactivity transient. 

Fig. 2. (— —) Cumulative and (—° —) 8% discounted cash flow rate for development of a hypothetical agrochemical in constant 1994 U.S. dollars, where A represents the time the patent was first issued B, first registered use C, manufacturing plant start-up D, positive cumulative cash flow and E, patent...

Production of propylene oxide in the United States in 1993 was estimated at 1,240,000 metric tons, and as having a 10-yr average aimual growth rate of 3.9% (229). Projections were for continued growth at about 4%/yr. Producers include Dow Chemical s chlorohydrin plants in Ereeport, Texas, and Plaquemine, Louisiana, and ARCO Chemical s hydroperoxide plants in Bayport and Chaimelview, Texas. Texaco started up a 180,000-t/yr plant in Port... 

Volumetric heat generation increases with temperature as a single or multiple S-shaped curves, whereas surface heat removal increases linearly. The shapes of these heat-generation curves and the slopes of the heat-removal lines depend on reaction kinetics, activation energies, reactant concentrations, flow rates, and the initial temperatures of reactants and coolants (70). The intersections of the heat-generation curves and heat-removal lines represent possible steady-state operations called stationary states (Fig. 15). Multiple stationary states are possible. Control is introduced to estabHsh the desired steady-state operation, produce products at targeted rates, and provide safe start-up and shutdown. Control methods can affect overall performance by their way of adjusting temperature and concentration variations and upsets, and by the closeness to which critical variables are operated near their limits. 

Sludge-blanket clarifiers are difficult to start up because the first blanket must be estabUshed, and large-scale units require extensive excavation. Sizes range from 600 x 600 mm to 50 x 50 m. Precipitation and crystallization can be carried out in similar hopper-designed units, having overflow rates of 80 m/h or higher. 

Raw material costs should be estimated by direct computation from flow rates and material prices. The flow rates are deterrnined from flow sheet material balances. The unit prices are obtained from vendors, company purchasing departments, or the Chemical Marketing Reporter. For captive raw materials produced internally, a suitable transfer price must be estabHshed. Initial catalyst charges can be treated as a start-up expense, working capital component, or depreciable capital, depending on the expected catalyst life and cost. Makeup catalyst is frequendy treated as a raw material. 

The magnetic field rotates at a synchronous speed, so it should also rotate the rotor. But this is not so in an induction motor. During start-up, the rate of cutting of llux is the maximum and so is the induced e.m.f. in the rotor circuit. It diminishes with motor speed due to the reduced relative speed between the rotor and the stator flux. At a synchronous speed, there is no linkage of flux and thus no induced e.m.f. in the rotor circuit, consequently the torque developed is zero. 

This is a vital relationship, which reveals that during start-up and until such speed, the reactance of the motor windings / 2> the rotor current will also remain almost the same as the starting current and will fall only at near the rated speed. (Refer to the current curves in Figures 1.5(a) and (b)). The initial inrush current in a squirrel cage induction motor is very high. In a slip-ring motor, however, it can be controlled to a desired level. (Refer to Section 5.2.1.)... 

Because of heavy start-up inrush eurrents, the use of LT motors should be preferred up to a medium sized ratings, say, up to 160 kW, in squirrel eage motors and up to 750 kW in slip-ring motors. For still higher ratings, HT motors should be used. 

I. A CMR motor therefore can be operated at higher outputs on short-time duties as shown in curve (d). The extent to which a CMR motor cun be over-rated to perform a particular short-time or intermittent duty is considered in the follow ing example. While evaluating the rating for such duties, the heat during start-up and during braking and their frequency of occurrence should be considered. 

During start-up, the motors must be suitable for accelerating to 80% of the rated voltage. 

Starting up the turbocompressor installation of a nitric acid plant does not present a problem. As mentioned earlier, during the startup phase the expander is not able to contribute any power. Accordingly, electric motor drivers must initially provide power in excess of the nominal operational rating. 

PROJECT UNIT APPUCATION P1(PSIA) T2 ( F) Rated kW LOCATION START-UP DATE AMB SUPPLIER AMB SYSTEM... 

---