Page 206 - Air and Gas Drilling Manual

5-48 Air and Gas Drilling Manual
In Illustrative Example 5.2b it was found that the actual shaft horsepower
required by the compressor to compress air to 284.1 psia was 193.2. The derated
horsepower available from the prime mover was 340.4. The prime mover for this
rotary compressor is also used to operate the hydraulic pump that operates the top
drive system. Thus, to obtain the fuel consumption for this prime mover (using fuel
consumption calculations outlined in Chapter 4) the power usage to operate the top
drive system must be estimated and added to the compressor horsepower usage. For
this example, it is estimated that the torque applied to the top of the drill string is
approximately 2,000 ft-lb at a rotary speed of 60 rpm. The horsepower required at
˙
the top drive system (at top of drill string), W , is [3]
td

Figure 5-10: Compressor output pressure and drill string injection pressure for
Illustrative Example 5.2c.