District Energy, 2007, 4th Quarter - Sample Partial Issue

Feature
Story
It’s Academic:
The case for coal gasification
on campus

Kevin Rhodes, PE, Manager, Energy Utilities Group, Woolpert Inc.

Owners of industrial-scale district energy heating plants, including academic institutions, are caught between the proverbial rock and a hard place. Within the past few years, natural gas prices have soared, while regulatory pressure has increased on owners with solid fuel-burning boilers – specifically in the form of the ‘MACT hammer,’ the maximum achievable control technology standards in Section 112(j) of the U.S. Clean Air Act, which takes effect in September 2007.

So what is the best fuel source for a college or university with either an existing central heating plant or plans to build a new one? There are many alternatives to consider, including biomass, methane, wastewater treatment plant digest gas and coal gasification. A mature technology with applicability on the industrial scale, coal gasification can be implemented at the same initial cost as natural gas and at lower operating costs – without the regulatory issues associated with burning solid coal.

Determining coal gasification’s economic viability for a particular owner involves exploring a number of factors, including the owner’s load profile, the availability of relatively high-sulfur coal and the cost of electricity. This is achieved by completing a feasibility analysis.

Coal Gas Production

To produce synthetic gas from coal, the raw coal is fed to the gasifier either in dry form or slurry. It reacts with steam and air or oxygen at high temperature and pressure, yielding a synthetic gas composed primarily of hydrogen and carbon monoxide and smaller quan-

tities of carbon dioxide and methane. The gasifier also converts the inorganic materials in the coal into a vitrified material, which can be sold in the construction market. The gas can be used to fire a boiler or as a fuel in an integrated gasification combined-cycle (IGCC) power generation configuration.

Figure 1. Strategies for the ‘Take-or-Pay’ Scenario. The ideal operating strategy in a ‘take-or-pay’ scenario is to operate at steady-state at the capacity of the gasification plant. This is rarely possible. The steam or gas demand must be manipulated to approximate the ideal condition, either by adding non-heating loads in the summer 'trough' or base loading.