In North America this year, unscheduled fuel shortages and fuel conservation interruptions led to significant shutdowns at gas turbine power plants. The most notable of these took place in Texas when freezing temperatures knocked out the power supply across the state from 14 – 19 February 2021, leaving 4.5 million households without electricity.
On the other side of the Atlantic, in Nigeria, power cuts are a regular occurrence. The economic cost of power shortages in the country is estimated at around $28 billion annually – equivalent to two percent of its Gross Domestic Product. In May 2021, low pressure on the Escravos-Lagos Pipeline System (ELPS) left several gas turbine power plants with insufficient gas supply, leading to plant shutdowns and widespread power blackouts for more than seven days.
So, what do North America and Nigeria have in common to explain these power failures? It may seem strange to draw parallels, but incidents in both nations highlight the interdependence of the natural gas and power systems. Both countries are huge producers of natural gas with massive natural gas reserves, yet both experienced power failures due to gas supply and low-pressure issues.
Trunk pipelines require sufficient volumes of natural gas to be fed into the system within a specified pressure range to ensure that gas is delivered to all consumers along the pipeline as per the contracted quality and quantity. Gas compression stations are fitted at regular distances along the pipeline to regulate this pressure.
Gas turbines operate a continuous combustion process requiring a constant supply of gas within a limited pressure range to generate a consistent power output. A drop in pressure or supply can cause the plant to malfunction. When there is a drop in volume and hence pressure, high pressure off-takers such as gas turbine power plants, which require pressure of 20-60 bar(g), are unable to operate and so drop off as customers. Reciprocating gas engine power plants, on the other hand, can continue to operate since they require much lower gas pressure (6-12 bar(g)) to sustain full rated capacity.
“The Texas icing event is a worst-case example of a perfect storm,” explained Jussi Heikkinen, Growth & Development Director, Americas at Wärtsilä Energy. “Texas has the highest share of wind energy in the U.S. with nameplate capacity close to 21 GW. But when the freezing temperatures drove a sharp increase in demand for heating, the high atmospheric pressure during the ice storm caused a distinct fall in wind speeds and a drop in wind power generation; the Texas power grid was on the brink of collapse. The system operator applied widespread load shedding to all but emergency needs. As a result, oil and gas producers in the Permian Basin, who depend on electricity to power their operations, were left with no way to pump the natural gas that was needed more than ever to generate electricity. The result was a vicious cycle. Compressor stations that keep gas flowing through pipelines were knocked out by the power outages, and as gas pressure dropped, this knocked out utilities because of lack of fuel.”
In Nigeria, which has the largest gas reserves in Africa, gas is used to fuel more than 80% of the nation’s grid-connected power generation capacity. But the challenging conditions of the gas transmission and distribution system as well as a lack of storage facilities mean that supply shortages and insufficient pressure affect the reliability of the power supply. Wale Yusuff, Business Development Manager and Managing Director of Wärtsilä Nigeria explained, “From 28 – 30 May 2021, the low pressure on the ELPS left 3,000 MW of stranded power. The country’s major gas turbine power plants were forced to shut down due to reduced gas pressure. However, the Lafarge Ewekoro 100 MW engine power plant, which receives gas from the same backbone pipeline, remained fully operational.”
The flexibility of engine power plants means that they are an ideal solution when gas transmission and distribution systems are weak. They can operate with a large spectrum of gas qualities. An engine can use liquid fuels if the engine is based on dual-fuel technology. Liquid fuels can be stored on site to provide always available back-up capacity to absorb supply shocks. But they are also the perfect ally for grids with high shares of renewable electricity generation from wind and solar. Made up of multiple engine modules which can be turned-down or fired-up instantaneously, they can provide incremental electricity quickly. In addition to being robust and versatile to manage gas transmission disturbances, they can also adjust output quickly in response to the intermittent nature of the weather.
Wärtsilä engines can start up even when the grid has no power, which helps electric transmission grid operators match fluctuating power requirements and restore power after major storms. In addition, power plants based on engine technology tend to require significantly less water than similarly sized combined-cycle or simple-cycle gas turbine plants.
In the U.S. reciprocating engine power plants have been increasingly deployed to balance renewables. In Texas alone, which has the most wind electricity generation capacity in the country, there are 910 MW of Wärtsilä engine power plants, or 20 % of the total in the US.
“During the coldest period of the Texas ice storm, some 25 GW of outages, over half of the total capacity, resulted from insufficient gas supplies reaching power plants. Thanks to flexible engine technology the impact of the storm did not grow bigger,” Jussi Heikkinen concluded.
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