Chapter 15 Process 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 Exchangers The 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 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 Fig. 15-13(p.270) 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 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.