Zero Thermal Discharge In Hydrocarbon Storage Tanks
Storage tanks are commonly used to store liquid and gaseous substances in Industry. In the oil and gas industry, storage tanks are for bulk containment of products at different stages of the process. These include feedstock, intermediates (unfinished petroleum products that need further processing or blending) and finished products. Most often, the products are stored for a short period of time before being moved.
Types of storage tanks
Storage tanks can either be overhead or underground, depending on product characteristics and factors of safety. Storage tanks in the oil and gas industry are almost exclusively above ground. Sizes range from 5-10 m diameter and 10 -30m height. They are generally installed inside containment basins in order to contain spills in case of rupture of the tank. Vapor or gas tanks can be cylindrical or spherical in shape.
Storage of products in the Oil and Gas Industry
Steam plays a vital role in storage tanks for the oil and gas Industry as it helps to maintain the pumping temperature of the product at required levels. The table below gives an idea of the temperature ranges for pumping of different products and steam pressure needed to maintain that temperature.
However, it is often noticed that a lot of thermal energy in steam is lost due to :
- Absence of steam trapping
- Group trapping methods
- Wrong selection of Steam Traps
- Uneven heating of product
- High pressure steam supply
- Stall conditions
- Water hammering
- Condensate draining
- No flash recovery
| Product | Coil Heating Steam Pressure barg | Product Pumping Temp °C | Product Tracing Steam Pressure barg |
|---|---|---|---|
| Crude Oil (seasonal – when ambient temperature < 20 °C) | 3.5 – 4 | 30-65 | 3.5 – 4 |
| Bitument (Three different grades) | 13-18 | 135-170 | 13-18 |
| RCO (Reduced Crude Oil) | 3.5 – 4 | 90-100 | 3.5 – 4 |
| VGO (Vacuum Gas Oil) | 3.5 – 4 | 70-80 | 3.5 – 4 |
| IFO (Internal Fuel Oil) | 3.5 – 4 | 90-100 | 3.5 – 4 |
| VR (Vacuum Residue) | 3.5 – 4 | 100-110 | 3.5 – 4 |
| FO (Furnace Oil) | 3.5 – 4 | 60-70 | 3.5 – 4 |
| SLOP | 3.5 – 4 | 50-70 | 3.5 – 4 |
Achieving Zero Thermal Discharge
Proper designing and detailed engineering of the steam system with the right type of steam traps and flash and condensate recovery for hydrocarbon storage tanks is essential to ensure zero thermal discharge. The complete procedure includes
- Installation of the right steam trap as per the application
- Installation of individual trap for individual coils
- Rationalisation of steam pressure
- Evacuation of condensate against high back pressure
- Flash and condensate recovery
Benefits of Zero Thermal Discharge
- Reduced Steam Consumption
– Installation of steam traps at no trap location blocks steam and discharge condensate as soon as it forms, preventing continuous loss of steam.
– Rationalising steam to lower pressures for heating ensures that latent heat of steam is utilised. - No Water Hammering
– Heating requirement for each coil differs as each coil is at a different level. The condensate discharge pattern also differs accordingly. Installation of individual steam traps for each coil will eliminate uneven heating and water logging issues. - No Stalling
– A pump-trap combination will help to evacuate condensate during equal or negative differential pressure across the steam trap. - Increased Gross Refinery Margin by Recovering Flash Steam and Condensate
– Ball float steam trap ensures continuous discharge of condensate, and also overcomes issues of water logging and uneven heating.
– Proper flash recovery from pressurised condensate leads to lower steam generation requirements, thereby saving fuel.
– Proper condensate recovery ensures return of pure water i.e. pure DM water to the boiler house. It exponentially increases the condensate recovery factor and reduces load on the polishing unit.
