{"id":614,"date":"2019-07-10T00:14:26","date_gmt":"2019-07-10T10:14:26","guid":{"rendered":"http:\/\/ahualoa.net\/farmblog\/?p=614"},"modified":"2019-07-10T21:20:12","modified_gmt":"2019-07-11T07:20:12","slug":"biochar-pit-sizes","status":"publish","type":"post","link":"http:\/\/ahualoa.net\/farmblog\/2019\/07\/biochar-pit-sizes\/","title":{"rendered":"Biochar pit sizes and volume of production"},"content":{"rendered":"

It’s been\u00a0seven years since I posted anything to this blog, but it’s a reasonable place to put things I’ll want to refer back to, so…<\/p>\n

There are currently two biochar pits. Pit 1 is the original, and Pit 2 (built July 2015) is a larger pit which incorporates lessons learned from the first pit. I always fire both together.\u00a0 When the pit is fired then opened up later, there is a gap at the top with air and a few chunks of wood that were not fully charred, which are removed, leaving a depth of char which is less than the depth of the pit.\u00a0 Here are both pits, freshly opened, with the torrefied wood still in place:<\/p>\n

<\/a><\/p>\n

New item by Ben Discoe \/ Google Photos<\/a><\/p>\n<\/div>\n

And Pit 2, emptied:<\/p>\n

<\/a><\/p>\n

New item by Ben Discoe \/ Google Photos<\/a><\/p>\n<\/div>\n\n\n\n\n\n\n
<\/td>\nWidth (inches)<\/strong><\/td>\nLength<\/strong><\/td>\nDepth<\/strong><\/td>\nDepth of char<\/strong><\/td>\nCubic inches<\/strong><\/td>\nCubic feet<\/strong><\/td>\nCubic yards<\/strong><\/td>\nLiters<\/strong><\/td>\n<\/tr>\n
Pit\u00a01<\/strong><\/td>\n29<\/td>\n53<\/td>\n23<\/td>\n16<\/td>\n24592<\/td>\n14.2<\/td>\n0.53<\/td>\n403<\/td>\n<\/tr>\n
Pit\u00a02<\/strong><\/td>\n31<\/td>\n63<\/td>\n25<\/td>\n18<\/td>\n35154<\/td>\n20.3<\/td>\n0.75<\/td>\n576<\/td>\n<\/tr>\n
Total<\/strong><\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n59746<\/td>\n34.6<\/td>\n1.28<\/td>\n979<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

In terms of carbon<\/strong>, it is difficult to say how much C is present in this partly-crushed, loose char. A solid block of charcoal, a web search indicates, might be 13 lbs\/ft3. Another source, biochar-specific, says it could vary widely from 5\u00a0to 20 lbs\/ft3. Using a value of 10, that gives 346 lbs of carbon, equivalent to\u00a01270 lbs of CO2.\u00a0 By a (similarly, very rough) approximation of the carbon footprint of air travel, at 1 lb CO2\/mile, a flight from Hawaii to California (~2400 miles) would require two complete firings of the charpits to offset the flight emissions, or four complete firings for a round trip.\u00a0 This analysis does not include the other (relatively small) carbon costs of the charpits, including per-burn costs (small amounts of gasoline for chainsaw and log-splitter) and amortized costs (footprint of the bricks used to build the pits).<\/p>\n

In terms of time and money<\/strong>,\u00a0looking around on this island, the\u00a0approximate price of biochar is $150 per cubic yard.\u00a0 (That\u00a0equals\u00a0$5.55 per ft3, so a 5-gallon bucket (0.67 ft3) would be $3.70.)\u00a0 At that price, the pits produce $192 worth of char.\u00a0 Firing the pits takes around 4.5 hours (can be anywhere from 4 to 5 depending on many factors).\u00a0 There is also time spent unloading, as well as gathering, cutting, splitting, and moving the wood to the charpits; these hours are harder to estimate but we can imagine another 3 hours per amount of wood that goes into a firing.\u00a0 That gives around $25\/hour for the\u00a07.5 hours of labor involved in each batch of char.<\/p>\n","protected":false},"excerpt":{"rendered":"

It’s been\u00a0seven years since I posted anything to this blog, but it’s a reasonable place to put things I’ll want to refer back to, so… There are currently two biochar pits. Pit 1 is the original, and Pit 2 (built July 2015) is a larger pit which incorporates lessons learned from the first pit. I […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[],"class_list":["post-614","post","type-post","status-publish","format-standard","hentry","category-biochar"],"_links":{"self":[{"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/posts\/614","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/comments?post=614"}],"version-history":[{"count":9,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/posts\/614\/revisions"}],"predecessor-version":[{"id":623,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/posts\/614\/revisions\/623"}],"wp:attachment":[{"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/media?parent=614"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/categories?post=614"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/ahualoa.net\/farmblog\/wp-json\/wp\/v2\/tags?post=614"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}