Ethylene

MOGAS valves handle the complications from massive cracking operations in ethylene production

A colorless flammable gas with a faint sweet and musky odor when pure, ethylene is widely used in the chemical industry. More ethylene is produced than any other organic compound, mostly to make polyethylene for plastic bags and pipes.

The ethylene production process includes four main steps: cracking, quenching, compression and processing. Reliable shut-off valves are essential to maximize ethylene quality and yield, and to minimize emissions, equipment damage and shutdowns.

The primary heat exchanger valve is the first valve in the system that sees the full range of products of the massive cracking operation that just occurred upstream, from the lightest (methane) to the heaviest (coke). Valves in this main transfer line need to absolutely isolate during the de-coking cycle, typically monthly, until a unit-wide shutdown is necessary for maintenance, cleaning and refurbishment.

Process hazards include:

fugitive emissions of feedstock
toxic and corrosive gases, e.g, hydrogen sulfide
corrosive materials (iron oxide, iron sulfide) that causes stress cracking
high temperature swings from 850 to 350° F from furnace to quench towers that causes leaks and valve damage
high pressure steam up to 1500° F
coke buildup, where de-coking presents a fire hazard should the valve not provide reliable air-tight isolation

MOGAS valves protect equipment from the harsh conditions of ethylene production through design features:

bi-directional sealing for backflow protection to restrict coke build-up and leaks into lines
durable disc spring design is particle tolerant (vs multiple coil springs)
wide seats and sharp leading seat edges wipe ball clean of harsh naphtha feedstock and coke build-up
fire safe graphite packing and spiral-wound body gasket
Class V shut-off due to risk of fire and cavitation
process and customer-specific coatings
high cycles
tight shutoff

Typical Operating Conditions:

Temperature: -50 – 850° F (-45 – 454° C)
Pressure: 50 – 600 psig (3.4 – 41.4 bar g)

Ethylene Process Flow Diagram

Feed
Steam
Recycle Feed
Primary Heat Exchanger
Fuel Oil
Primary Fractionator Overhead
Cooling Distillation Tower Ethylene Cut
Cooling Distillation Tower Recycle
Cooling Distillation Tower Water
Cooling Distillation Tower Overhead
Cracked Gas Compressor
Pre-Fractionator
Caustic Wash Column
Pre-Fractionator Overhead
Caustic Wash Column Overhead
Drying Column
Main Cooler
Main Cooler Overhead
Hydrogen Separator Methane
Hydrogen Separator Hydrogen
De-methanizer
De-methanizer Overhead
De-ethanizer
De-ethanizer Overhead
Acetylene Hydrogenator
Hydrogen
Ethylene Separator
Ethylene Overhead
Ethylene Separator Bottoms
De-propanizer
De-propanizer Overhead
Methylacetylene Hydrogenation
Hydrogen
Propylene Splitter
Propylene Splitter Overhead
De-butanizer
De-butanizer C4 Overhead Fraction
De-penthanizer
De-penthanizer C5 Overhead Fraction
Gasoline Splitter
Gasoline Splitter C6-C9 Overhead

Heat Exchanger (not shown)
General Ball Valves (not shown)