© 2012 delmar, cengage learning chapter 15 process system hazards

© 2012 Delmar, Cengage Learning

Chapter 15Process System Hazards


Operating Hazards

• Equipment and systems

• Weather

• Chemistry and chemicals


Equipment and System Related Hazards

Pumps:

• Cavitation

• Vapor lock

• Improper line-up

• Variation in suction head or NPSH

• Gasket leaks

• Seal flush tubing plugs up


Figure 15-1 Pump Seal Leak


Cavitation

• The formation and collapse of air pockets inside the pumping chamber.

• Boiling

• Cavitation can be prevented by increasing the NPSH or pinching down on the discharge valve.


Pressure

• The force or weight per unit area.

• The higher the atmosphere, gas, or liquid the greater the pressure.

• Liquid pressure is exerted equally in all directions.

• Height of Liquid × 0.433 × specific gravity = pressure


Figure 15-2 Pump System


Compressors

• Watching flammability limits is important when equipment containing air is purged using gas. If gas enters too slow a flammable mixture is formed. If it enters too fast it can produce a spark.

• When selecting a gas to purge with piping line-up is critical.


Figure 15-3 Purging Procedure


Figure 15-4 Reciprocating Compressor


Common compressor safety issues:• Noise hazards• High-pressure hose blowing loose• Hazards associated with compressed gas

systems• Hazards associated with rotating equipment• Mixing air and hydrocarbons into flammable or

explosive concentrations• Avoiding high-pressure releases; eyes, nose• Fires or explosions• Incorrect line-up• Loss of cooling water• Lifted safety


Figure 15-5 Compressed Air System


Figure 15-6 Factor of 4 Safety Design


Heat ExchangersThe effects of absorbed heat:

• Increase in molecular activity• Change of state• Chemical change• Energy movement from hot to cold• Radiant heat transfer• Conductive and convective heat transfer• Electrical transfer – thermocouple• Increase in volume• Increase in temperature


Figure 15-7 Heat Exchanger System


• Process technicians use a variety of temperature systems. The four most common are K, °C, °F, °R.

• Heat is a form of energy caused by increased molecular activity that cannot be created or destroyed, only transferred.

• The hotness or coldness of a substance determines the temperature.

• Heat is measured in BTUs. Temperature is measured in K, °C, °F, °R.

• Heat and temperature are not the same.


Safety aspects associated with the operation of a heat exchanger system include:

• Chemical hazards associated with spills and leaks• Hazards associated with burns• Hazards associated with fires• Hazards associated with explosions and boiling liquid

expanding vapor explosion• Confined space entry• Equipment failure• Gauge failure• Sampling, purging, or venting the shell


Cooling Tower

Safety aspects of the cooling tower system include the following:

• Chemical additives• Rotating equipment• Hazards of hot water• Equipment failure• Working at heights• Hazards of working with acids• Confined space entry• Hazardous energy


Figure 15-8 Cooling Tower System


Furnace or Fired Heater

• In the instance of a flame-out, the concentration of hazardous gases can build up in the furnace until it explodes.

• Another common problem is tube leaks. Tube failures are typically related to flame impingement, high heat loads, or erosion.


Figure 15-9 Typical Fired Heater


Steam Generation• Accidental release of high-, medium-, and

low-pressure steam. • High-velocity steam can cut through solid

objects.• Steam can eat away the inner surfaces of

industrial equipment used to contain it.• Thermal warp, thermal shock, water hammer,

and thermal expansion are all natural phenomenon process technicians should be aware.


Figure 15-10 Steam Generation – Uses and Applications


Figure 15-11 Power Generation System


Electricity

• The hazards associated with electrical shock are severe and require specific training.

• Electrical equipment repair should be performed only by qualified plant electricians.


Flare System

• When a flare is smoking badly, this is an indication that the plant is having serious problems.

• Black smoke from a flare shows unburned hydrocarbons and the loss of company profits.


Figure 15-12 Flare System


The hazards associated with flare operation include:

• Flare pilot light goes out and heavy hydrocarbon vapors drop to the ground and seek ignition source

• Flare header overwhelms flare system and produces black smoke

• Fan motor catches fire• Pump goes out on knock-out drum liquid seal and

pressure increases on header• Steam ring fails• Support cable breaks during high winds and flare

falls


Weather-Related Hazards• Lightning is a common occurrence that

rarely finds an unprotected or ungrounded system in a plant. It is not safe to be on the tallest vessel or distillation column during a lightning storm.

• Heavy rain storms can quickly drop the temperature and cause wide variation swings in process variables.


• Freezing weather can also cause problems.

• Hurricanes present numerous hazards: high winds, flooding, power outage.

• The severity of the storm will determine the action plan the plant will use and how much of the facility will be shut down.


Chemicals and Chemistry Related Hazards

• Chemistry related hazards are associated with the way two or more chemicals will respond to each other under specific operational conditions.


Reactors

• Reactors are used to make new products by making or breaking chemical bonds.

• A reaction is either exothermic or endothermic.


Figure 15-13 Stirred Reactor


• Atoms are composed of positively charged particles called protons, an equal number of neutral particles called neutrons, and negatively charged particles called electrons.

• Valence electrons are important because they provide the link to almost every chemical reaction.

• Chemical bonding is classified as either ionic or covalent.


• Matter is anything that occupies space and has mass. The four physical states of matter are solid, liquid, gas, and plasma.

• A compound is defined as a substance formed by the chemical combination of the two or more substances in definite proportions by weight.

• A mixture is composed of two or more substances that are only mixed physically.


• In a chemical reaction, the raw materials or reactants are placed on the left side. As the reactants are mixed together, they yield predictable products. The products are placed on the right side of the equation.

• What goes into a chemical reaction must come out.


Safety hazards associated with the operation of a stirred reactor include:

• Runaway exothermic or endothermic reaction• Feed composition changes cause rapid

pressure changes• Fee concentration increase – reaction becomes

unstable• Agitation problems will reduce reaction• Loss of cooling water• Loss of catalyst• Temperature increase – doubles reaction rate

for every 10°C increase


Distillation System

• Operational hazards associated with distillation include the following:

• Fires and explosions• Leaks – gasket, valve, instruments, piping, and

pumps• Pressure surges• Loss of cooling water• Steam valve stuck in open position• Exothermic reaction occurs in the column• Instrument failure


Human Factors

• Human error has been identified as the most common cause of industrial accidents.

• A technician’s greatest nemesis is fatigue and mental stress. Most of the biggest industrial disasters have taken place between the hours of 1:00 A.M. and 4:00 A.M.

© 2012 delmar, cengage learning chapter 15 process system hazards

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