Page 285 - Compression Machinery for Oil and Gas

270 SECTION II Types of Equipment

FIG. 6.15 Balanced carbon ring seal.

FIG. 6.16 Carbon ring seal with separation.

sealing medium. If the buffer gas fails, the compressor must be depressurized
immediately in order to prevent leakage of process gas. The carbon rings are not
gastight and therefore a certain leakage to flare or to the oil reservoir is unavoid-
able during depressurization.
Fig. 6.17 shows a water buffered restrictive ring-type seal. This is a good
choice for dry screw compressors operating with dirty and dusty gases like coke
oven gas, lime kiln gas, or acetylene crack gas which require injection of large
amounts of demineralized water for cooling and washing purposes. In these
cases, the discharge temperature is somewhat below saturation temperature
so that a certain amount of water leaves the compressor in the liquid form.