Scale, capacity and feedstock: which chemical plants get built

By the end you will be able to

• Apply the six-tenths rule to estimate how capital and cost per tonne change with plant size
• Explain the technical, financial and safety limits to plant scale and when small plants still win
• Analyse how plant sizing, timing and utilisation drive the chemical industry's boom-and-bust cycle
• Compare how feedstock prices for ethane, naphtha, gas and coal give regions a lasting cost advantage
• Evaluate how integration, uncertainty, safety requirements and green chemistry metrics change investment decisions

Contents

1. Part 1 Economies of scale: why big plants make cheap tonnes

   A chemical plant twice the size does not cost twice as much to build or staff, but it needs twice the raw material. That asymmetry explains why commodity chemicals are made in very large plants and why small plants usually lose. This part shows where the rule comes from, puts numbers on it with a sulphuric acid plant, and shows which cost lines it touches.

   • Capacity grows with volume while cost grows with surface, so bigger units are cheaper per tonne
   • A worked example: one sulphuric acid design at three sizes
   • Scale matters most where fixed costs dominate the cost sheet
2. Part 2 How plant sizes grew, and what stops them growing

   From the 1950s to the early 1970s the largest new plants for ethylene, ammonia and other bulk chemicals grew several times faster than the markets they served. Then growth slowed sharply. This part puts numbers on the scale histories, sets out the technical, financial and safety limits to size, and explains why small plants still survive in some places.

   • For three decades the biggest plants grew faster than their markets
   • Equipment limits, capital, project risk and hazard put a ceiling on size
   • Small plants survive where the market, freight, hazard or a feedstock protects them
3. Part 3 Capacity planning, utilisation and the chemical cycle

   Capacity arrives in large lumps years after the decision to build it, while demand grows smoothly and unpredictably. Getting the size and timing right decides whether a plant runs full or sits half empty. This part covers the plant-size decision, why utilisation matters so much, how existing plants creep up in capacity, and why the whole industry tends to overbuild at the same time.

   • Capacity comes in lumps, so choosing a plant size is a bet on future demand
   • Utilisation decides whether a big plant's cost advantage is real
   • Existing plants creep up in capacity, but rarely catch new world-scale plants
   • Across the industry, firms tend to build at the same time, and the cycle follows
4. Part 4 Technology, learning and feedstock: where the cost floor is set

   Scale and utilisation decide how efficiently a plant spreads its fixed costs. Technology and feedstock decide what those costs are in the first place. This part looks at how process technologies improve and get replaced, why feedstock prices give some regions a lasting edge, and how the IEA's scenarios might redraw the map of where ethylene, ammonia and methanol get made.

   • Technologies follow S-curves, and experience lowers costs only up to a point
   • Feedstock price is the main reason one region's plant beats another's
   • Ethane gives the cheapest ethylene, naphtha the broadest product slate, and scenarios may shift the map
5. Part 5 Integration, uncertainty, safety and sustainability: what decides what gets built

   A plant with good scale, technology and feedstock can still fail if it stands alone, ignores risk, or cannot meet safety and environmental demands. This part looks at why chemical plants cluster, how companies test investments against uncertainty, how safety rules and accident costs shape design, and how green chemistry metrics and carbon costs are entering the cost sheet.

   • Integration and clusters cut capital, storage, freight and risk
   • Uncertainty is handled with sensitivity tests, scenarios, staged options and portfolios
   • Safety rules and accident costs shape plant size, inventory and siting
   • Green chemistry metrics and carbon costs are entering the cost sheet
6. Wrap-up Key terms, try it in the table, final quiz, sources