JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV NATURAL GAS PROCESSING Previous Question Paper (February/March - 2022 - R18)

Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, with varying amounts of other higher alkanes and small percentages of nitrogen, carbon dioxide, hydrogen sulfide, or helium. It originates from organic matter buried deep within the Earth's crust over millions of years, subjected to intense heat and pressure.

Sources of Natural Gas:

1. Associated Gas: Found in petroleum reservoirs, this gas is dissolved in crude oil or exists as a cap of free gas above the oil.
2. Non-Associated Gas: Found in reservoirs that contain little or no crude oil, often referred to as gas fields.
3. Coal Bed Methane (CBM): Natural gas trapped within coal seams, adsorbed onto the surface of the coal matrix.
4. Shale Gas: Gas trapped within fine-grained sedimentary rocks (shale formations) with low permeability, requiring hydraulic fracturing for extraction.
5. Tight Gas: Gas found in reservoirs with extremely low permeability, requiring advanced stimulation techniques.

Scenario and Resources in India:

India's natural gas sector is a critical component of its energy mix, as the government aims to transition toward a gas-based economy. The current scenario is characterized by a significant gap between domestic production and consumption, necessitating substantial imports of Liquefied Natural Gas (LNG).

Key Resources and Regions:

• Offshore Basins: The Krishna-Godavari (KG) basin, specifically the KG-D6 block, is a major production hub. Other significant offshore areas include the Mumbai High basin and the Cauvery basin.
• Onshore Basins: Major onshore production occurs in the Assam-Arakan basin and the Cambay basin in Gujarat.
• Unconventional Resources: India has significant potential in CBM, with active blocks in the Raniganj, Jharia, and Bokaro coalfields. Exploration for shale gas is also underway in several sedimentary basins.

Despite these resources, India relies on imports from countries like Qatar, the USA, and Australia to meet industrial, power generation, and city gas distribution (CGD) demands. The expansion of the National Gas Grid and the development of LNG regasification terminals are ongoing strategic initiatives to enhance energy security and improve gas availability across the country.

A natural gas processing plant is a complex facility designed to purify raw natural gas extracted from underground reservoirs. The primary objective is to remove impurities and non-methane hydrocarbons to meet pipeline quality specifications and recover valuable natural gas liquids (NGLs).

The processing overview involves several key stages:

1. Separation: Initial removal of free water, condensate, and solids using separators or scrubbers.
2. Acid Gas Removal: Sweetening the gas by removing hydrogen sulfide (H₂S) and carbon dioxide (CO₂) using chemical solvents like amines to prevent corrosion and meet environmental standards.
3. Dehydration: Removing water vapor using glycol units or molecular sieves to prevent hydrate formation and pipeline corrosion.
4. NGL Recovery: Extracting heavier hydrocarbons (ethane, propane, butane, pentanes) via refrigeration, cryogenic expansion, or absorption processes.
5. Fractionation: Separating the recovered NGL stream into individual high-purity product components.

Safety and environmental considerations are critical due to the hazardous nature of the substances handled:

Safety Considerations:

• Leak Detection and Mitigation: Implementation of automated gas detection systems and emergency shutdown (ESD) valves to isolate sections during leaks.
• Pressure Management: Use of pressure relief valves and flare systems to prevent catastrophic vessel failure during overpressure events.
• Fire Protection: Installation of deluge systems, fire monitors, and foam suppression systems, alongside strict adherence to hazardous area classification (ATEX/NEC) for electrical equipment.
• Personnel Safety: Mandatory use of personal protective equipment (PPE), rigorous training on H₂S protocols, and regular safety drills.

Environmental Considerations:

• Emission Control: Minimizing methane leaks (fugitive emissions) through regular LDAR (Leak Detection and Repair) programs and utilizing vapor recovery units.
• Waste Management: Proper treatment and disposal of spent amines, glycol, and produced water, which may contain heavy metals or hydrocarbons.
• Flaring Reduction: Optimizing plant operations to minimize routine flaring, thereby reducing greenhouse gas emissions and noise pollution.
• Regulatory Compliance: Adherence to local and international environmental standards regarding sulfur recovery efficiency and air quality monitoring.