Urea…yes…a primary waste product of urine is actually a key ingredient to reducing nitrogen oxides or NOx emissions from diesel engines. NOx is a by-product of combustion, and is the primary cause of smog, acid rain, and the production of ozone. Not only does NOx not take too kindly to the atmosphere, it also does not take kindly to humans. NOx and various toxic by-products from reactions with NOx cause lung irritation, and in high enough concentrations permanent lung damage and biological mutations.
It also just so happens that large marine diesel engines produce a heck of a lot of NOx. I do mean a lot. In fact, here are some key figures:
- 15 of the world’s largest ships emit as much contaminates as all of the world’s 760 million cars
- It is estimated that the pollution from the world’s 90,000 cargo ships leads to the death of 60,000 people/year worldwide.
- Cars driving 15,000km a year emit approximately 101 grams of sulfur oxide gases (or SOx) in that time. The world’s largest ships’ diesel engines which typically operate for about 280 days a year generate roughly 5,200 tonnes of SOx.
- Shipping is responsible for 18-30% of all the world’s nitrogen oxide (NOx) pollution and 9% of the global sulfur oxide (SOx) pollution.
One might argue that there are many power plants and industrial facilities that would have to fall ahead of ocean going ships in the list of the world’s most severe air polluters, but not so fast. To save on fuel costs, ocean going ships still use some of the lowest grade fuel (Heavy Fuel Oil) which has a high sulfur content and does not burn as clean as diesel used in trucks and other applications ashore. The unpredictable operating nature of diesel engines aboard ships also presents a challenge in designing appropriate emission control applications. Most large boilers, and power plants ashore have extensive emission control devices, that have been relatively easy to install and maintain with very few size/weight constraints, no intrusive salt water, and much more predictable engine load/exhaust temperatures.
In order to meet EPA regulations, operators of marine diesel engines have turned to using urea in Selective Catalytic Reduction (SCR) systems to reduce NOx emissions. SCRs have been used extensively in large municipal power plants, and are even widely found in European automobiles. Essentially, liquid urea is sprayed into the exhaust after it leaves the engine, and then passes through a catalyst box containing some type of a metal catalyst where a chemical reaction occurs that converts NOx into harmless diatomic Nitrogen and H2O. CO2 is also a by product of the reaction when urea is used.
Some U.S. marine operators are moving ahead to confront the emissions problem by installing experimental equipment to determine feasibility and efficiency of various emissions control applications. Matson Navigation has installed an SCR for post treatment of exhaust from a diesel generator on a C9 class container ship. APL has installed a water injection system to reduce NOx from the main engine of a C11 class container ship, and has tested going cold iron in port with localized power generation using generators run on LNG.
Large ships are not the only ones effected by emission regulations. Virtually every commercial marine operation is already or will be effected at some point by emission regulations. Operators in California are seeing this first hand. The Bay Area commuter ferry M/V Solano has been operating with a urea injection SCR system and their are plans to outfit several other commuter ferries with similar equipment.
The bottom line – emission control is going to be huge. Besides the economy and fuel prices, emission reduction and control will heavily occupy the marine engineering field for the foreseeable future and beyond. Emission control certainly comes at a price…a heavy price. Not only do you have the installation and maintenance costs, but so far, fuel economy has also suffered in many of the test platforms. Urea is also a substantial expense. The commuter ferry Solano found that their SCR installation resulted in approximately $100k/year in urea expenses.
Have you already seen changes on board your ship? How has emission control effected your job or your engine plant? Share it here!