Design conditions

Some examples for design conditions presented in Corps publications follow. ER 1110-2-1404, Deep-Draft Navigation Projects Design (USAGE 1981), states  

The following weather and hydraulic factors are needed for input to the navigation project design analysis. 

EM 1110-2-1615, Hydraulic Design of Small Boat Harbors (USAGE 1984), refers to design conditions as follows  

The design of a small boat harbor project will require an analysis and evaluation of information on the following  

Currents (Tidal, River, Seiche, Wave Generated) 

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Table 1. Typical Industrial Inside-Design Conditions ...

Listed conditions are typical final design conditions are established by customer requirements. 

Specific inside design conditions are required in industrial applications for one or more of the following reasons ... 

The temperature and humidity should be maintained at comfort conditions consistent with the operator s expected level of activity in order to minimise perspiration. Constant temperature and humidity may also be required in machine rooms to prevent the etching or corrosion of machine parts. If perspiration causes only minor damage to the product and results in few rejects, then inside design conditions at 27°C and 40% rh are satisfactory. Where even small amounts of perspiration cause extreme damage to precision-machined parts and result in a high amount of rejects, inside design conditions of 21°C and 40% rh are recommended. 

Conditions of high pressure and low temperature favor the formation of the complex, whereas low pressure and high temperature tend to release the complexed carbon monoxide from solution. These conditions typify the operation of the absorber-stripper shown in Figure 2. Specific design conditions for the process are given in references 86—88, and an excellent summary of processing considerations is presented in reference 85. 

The product gas after cleanup consists of primarily CO and H2. Combustion of coal gas in high firing-temperature gas turbines converts virtually all of the CO to CO2, and gas turbine exhaust is expected to contain no more than 10 ppm CO when operating at design conditions. Carbon monoxide emissions from a CGCC plant are thus expected to be around one-tenth those of a modem coal-fired plant equipped with low NO burners. 

Design Conditions Definitions of the temperatures, pressures, and various forces applicable to the design of piping systems are as follows ... 

Occasional variations above design conditions shall remain within one of the following limits for pressure design ... 

In spht-flow shells the longitudinal baffle may be installed without a positive seal at the edges if design conditions are not seriously affected by a hmited amount of bypassing. 

Operating co.sts. Power requirements for air-cooled heat exchangers can be lower than at the summer design condition provided that an adequate means of air-flow control is used. The annual power requirement for an exchanger is a function of the means of airflow control, the exchanger seiwice, the air-temperature rise, and the approach temperature. 

When the mean annual temperature is 16.7°C (30°F) lower than the design dry-bulb temperature and when both fans in a bay have automatically controllable pitch of fan blades, annual power required has been found to be 22, 36, and 54 percent respectively of that needed at the design condition for three process services [Frank L. Rubin, Tower Requirements Are Lower for Air-Cooled Heat Exchangers with AV Fans, Oil Gas J., 165-167 (Oct. 11, 1982)]. Alternatively, when fans have two-speed motors, these dehver one-half of the design flow of air at half speed and use only one-eighth of the power of the full-speed condition. 

Design conditions range in pressures from full vacuum to 96.5 bar g and in temperatures from —269°C to 200°C. This is accomphshed meeting the quality standards of most pressure vessel codes. 

Ultimately, the economic choice between counterflow and cross-flow is determined by the effectiveness of the fill, design conditions, and the costs of tower manufacture. 

Example 12 Application of Sizing Chart Assume the same cooling range and approach as used in Example 11 except that the wet-hiilh temperature is lower. Design conditions would then he... 

When no chemical reactions are involved in the absorption of more than one soluble component from an insoluble gas, the design conditions (pressure, temperature, and liqnid-to-gas ratio) normally are determined by the volatility or the physical sohibility of the least soluble component for which complete recovery is economical. Components of lower volatihty (higher solubility) also will be recovered completely. 

Consider the possibility of developing for the new system a rigorous, theoretically based design procedure which will be valid over a wide range of design conditions. 

For the design condition, F-factor is 2.08 n l/sfkg/m ), or about 76 percent of flood. The proposed column is entirely adequate for the service required. 

Operational reliability Also known as equipment reliability. The probability that, when operating under stated design conditions, process equipment will perform its intended function adequately for a specified exposure period. 

Most ethylene plants operate continuously with the expanders operating at or near design conditions. If necessary, due to their unique design characteristics, radial inflow turboexpanders can accommodate a wide range of process conditions without significant losses in thermal or mechanical efficiency. Expanders may be loaded with booster compressors, gear-coupled generators, dynamometers, or other in-plant mechanical equipment such as pumps. In ethylene plants, turboexpanders are typically used in eitlier post-boost or pre-boost applications. 

In the following discussion on TTE degradation, it is assumed that for constant speed cases the turboexpander drives an induction generator and for variable speed cases it drives a compressor with normal design conditions as given in Table 7-8. 

Consider the sensitivity of TTE to four process gas normal design condition parameters inlet gas pressure (P ), inlet gas temperature (Tj), gas mass flow (M), and gas molecular weight (MW). 

Clearly, the turboexpander is one of several key components in a process plant and liquid production is related to the performance of all components of the plant, not the turboexpander alone. It has previously been assumed that changes in the normal design conditions of turboexpanders have not adversely affected other equipment in the plant because adverse impact on other equipment, if any, would further reduce liquid production. This simplifies the assumptions, but does not affect the general validity of the findings. 

Most ethylene plants operate continuously with the expander functioning at or near design point. However, by using inlet guide vanes, the expander can still provide optimum performance at off-design conditions. Also, the expansion process generates power, which is used by the compressor. The ethylene enters the expanders at approximately 26 bar (377 psia) and exits at approximately 6 bar (87 psia). The expanders generate over 2,000 hp for gas compression. 

CASE 14 IMPROVING FCC EXPANDER RELIABILITY UNDER OFF-DESIGN CONDITIONS ... 

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